Fluid Mechanics and Fluid Power – Contemporary Research

A Direct numerical simulations (DNS) is carried out to study the highly three-dimensional flow field around a jet coming out of a stack and interacting with the cross-flow passing it. The major objective of the study is to assess the effect of shear strength of inlet velocity on the wake behavior and structures for elevated jets in cross-flow (EJICF). All the simulations are carried out for a Reynolds number of 250 based on the averaged inlet velocity and width of the stack and the blowing ratios considered are 0.5, 1.0 and 1.5. Effect of shear strength (0.025, 0.050 and 0.075) of inlet velocity is studied by solving the incompressible unsteady 3-D Navier-Stokes equations using a second order discretization for space and time. The solution algorithm is based on MAC method. The dynamics of flow associated with the flow field, like different wakes zones present in the flow are discussed with respect to the shear strength of free stream velocity. The vortical structure associated with EJICF is also studied.

The momentum transfer characteristics of slip flow around an assemblage of spherical particles in a shear-thinning fluid (n = 0.6) is numerically studied. At fluid-solid interface a linear slip velocity is applied. As the non-dimensional slip number (λ) increases, the fluid slip becomes weaker i.e., λ = 0 represents fully slip flow and λ = ∞ indicate no-slip velocity at the solid-fluid interface. A finite difference method based on SMAC semi-implicit algorithm is used in this work over the range of conditions as: Reynolds number, Re = 100–200, power-law behavior index, n = 0.6, volume fraction of slip spheres, Φ = 0.1, and dimensionless slip parameter, λ = 0.01–100. Finally effects of these parameters on detailed flow kinematics are discussed in details.

The experimental methodology to perform droplet size distribution of Liquid Centered Swirl-Coaxial injector (LCSC) using simultaneous Planar Laser-Induced Fluorescence (PLIF) technique and MIE scattering is demonstrated. The fluid used for spray characterization is water with required quantities of the organic dye Rhodamine 6 g for PLIF measurements. The injector performance is evaluated in terms of relative droplet size distribution and spray divergence angle. The droplet size distribution indicated that the relative SMD of droplets along the axial location of the spray is uniform throughout. It is also observed that the improved performance in spray divergence angle could be achieved by recessing the height of liquid passage with reference to the oxidizer.

Coalescence is a process in which two or more drops contact each other and merge to form a single daughter drop. The process may occur in a fluid medium or on a solid surface. In both instances, coalescence is an intense dynamic process during which the fluid is momentarily set into motion. The present study compares the shear rates, and hence, shear stresses generated on the wall because of the coalescence of two drops in pendant and sessile configurations. In experiments, two drops of equal volume are placed adjacent to each other till a liquid bridge is formed with the drops just touching each other. The equilibrium contact angle considered is 110o. The liquid is water placed on and underneath a textured surface. Coalescence is driven by the negative curvature of the liquid bridge, leading to a pressure difference. The contact line moves and bridge relaxes as flow takes place from a region of higher to lower pressure. The entire process has been imaged by using a high speed camera. The image sequence is analyzed to find the instantaneous center of mass of the drop, which in turn, yields the velocity components. These are used to find the time-dependent wall shear rates. Experiments show that two timescales appear during the merging of the drops. Large shear stresses are momentarily developed at the wall with a magnitude that depends on the drop volume. Oscillations in the drop shape are stronger in the pendant configuration where gravity is an additional driving force.

A study is conducted on supersonic flow at Mach number 1.65 over rectangular cavity of length-to-depth (L/D) ratio 3. Schlieren visualization revealed normal shock train like pattern in flow over the cavity. These shock structure are unsteady, and oscillated longitudinally inside the test section over the cavity. The oscillating shock train is eliminated, as the blockage produced by shear layer and boundary layer thickening due to pressure recovery in cavity is reduced by offsetting the cavity aft wall. The shock train—shear layer coupling is observed to completely suppress the third and higher modes of cavity oscillations.

The interaction of vortex rings with free surface is of considerable interest to the water vehicles like ships and other vehicle, which moves close to the water surface. The perturbation in the surface may also be useful for various applications. The Effect of free surface height on the submerged synthetic jet parallel to the surface in quiescent flow is studied experimentally. Flow visualization using Laser Induced Fluorescence (LIF) and mean stream wise and cross-stream wise velocities are taken by 5-Beam Laser Doppler Velocimetry (LDV) probe. This study is related to understand the vortex ring structure of synthetic jet and its effect on the free surface of water. Parameters for this study are, orifice diameter 13 mm at actuation frequencies 1 and 6 Hz. Three different water levels H = 1.5D, H = 3D and H = 5D from the center of the orifice are used for this study. Due to change in free surface height (H), it is observed that at frequency 1 Hz and water depth H = 1.5D, vortex rings drifted towards the free surface and create transverse surface waves during the interaction. Rebounding of vortex rings are also seen at frequency 6 Hz and water depth H = 1.5D. Velocity analysis shows that velocity normal to the surface reduces and velocity parallel to the surface increases as the vortex ring approaches the free surface. Previous studies on jets also suggest similar phenomenon for submerged jets.

A detailed experimental study has been done to understand the shock wave-turbulent boundary layer interaction (SWTBLI) over a forward-facing step (FFS) of height (h) in a Mach 2.5 flow using particle-image velocimetry (PIV). In addition to PIV, high-speed schlieren and surface oil flow visualization have been studied. Flow separation using surface oil flow visualization was observed around 4.1 step heights upstream of the step face. High-speed schlieren measurements show that the shock oscillates with a peak frequency of approximately 1000 Hz, which is two orders smaller than the characteristic frequency of the incoming boundary layer. Instantaneous PIV velocity vector fields show that the shock location is related to the separation bubble formed ahead of the forward-facing step.

Boundary layer separation is the principal cause for the relatively large drag force experienced by a bluff body undergoing uniform motion in an otherwise quiescent fluid. Active and passive flow control strategies which effectively suppress or prevent flow separation are of considerable practical importance as they can facilitate drag reduction and efficient propulsion in mechanical systems like underwater robotic and micro air vehicles. In this work we present a comparative investigation of two popular flow control strategies that rely on normal and tangential surface distortions in order to achieve a reduction in the total drag experienced by a translating circular cylinder. The energetic efficiency of the flow control strategies is quantified using the power loss coefficient; a metric of performance that is directly linked to the net power consumption. The efficacy of the tangential and normal surface distortions based flow control strategies is evaluated and compared using the effective reduction in the hydrodynamic forces and net power consumption in the laminar flow regime. Simulations indicate that the tangential boundary motions are slightly more effective than normal distortions in reducing the total drag on circular cylinder.

Arid regions, like Rajasthan, receive abundant solar energy and are prone to dust/sand storms. Line and point focusing technologies are used for harnessing this energy. At IIT Jodhpur, open porous volumetric air receiver based point focusing technology is considered for process heat application. This system uses air as heat transfer fluid and is expected to achieve a temperature as high as 800 °C. This receiver on account of volumetric heating, is exposed to a high heat flux, even, up-to 1000 suns (1sun = 1 kW/m2). As this receiver is open to atmosphere, the dust storms in these regions can block the absorber pores and enter the system. Due to lower thermal conductivity of sand in comparison to absorber material, high temperature gradients and thermal stresses are expected on the absorber. It can result in failure of the system. In view of this the current activity aims at cleaning and collection of the removed dust from pores of receiver. A 2D2D geometry of cyclone separator is proposed for deposited dust collection. The experiments on collection efficiency and pressure drop are performed and compared with empirical model. Pressure drop is estimated using CFD and experimentally validated for an improved relation for pressure drop coefficient.

Numerical inspection concerning to alleviate the effect of Counter Rotating Vortex Pair (CRVP) adopting delta winglet type vortex generators (VGs) has been contemplated in present study. The jet to cross flow blowing ratios is investigated at 2, while Reynolds number based on jet velocity and film-hole diameter is kept at 4700. Two different geometric configurations are considered. With the absence of Delta winglet pair (DWP) a single 35° inclined holes on a horizontal bottom surface of mainstream flow (primary flow) domain, is chosen for baseline case. While base line with Common-flow-up (CFU) arrangement of DWP, is preferred as another one. The numerical investigation is executed with FLUENT commercial code implementing the k-ε model. Computational investigation represents that contemporary procedure enhances the film cooling by creating opposite vortices to CRVP. These obverse vortices, created from CFU DWP configurations, assist in maintaining the jet flow adjacent to the bottom wall of mainstream domain.

In the present investigation, the effect of aeration rate on bed hydrodynamics in the riser of a pressurized circulating fluidized bed (PCFB) has been studied. Experiments are conducted with two different bed inventories, viz. 500 and 750 g. Aeration superficial velocities, U _sup = 0.65, 1.94, and 3.23 m/s respectively are used to observe the change of bed hydrodynamics of the PCFB. Operating velocities of 2.72, 3.4 and 4.08 m/s and pressures of 100, 200, and 250 kPa are maintained for each inventory and aeration rate. It has been observed that the suspension density increases along the riser height with the decrease in aeration rate. The solid circulation rate increases with the increase in aeration rate as well as primary air flow rate. The present study will help in optimizing the aeration rate for smooth operation of the non-mechanical valve or the stand pipe without obstruction of inventory material.

Direct Numerical Simulations (DNS) based on MAC Method are performed at different Reynolds numbers and blockage ratios. DNS helps in predicting flow field, variation of drag coefficient, non-dimensional frequency called Strouhal number at different values of Reynolds number and blockage ratios. The study is performed at different blockage ratios ($$ \beta $$β), ranging from 0.1 to 0.9, to study the effect of blockage ratios on fluid flow stability and critical Reynolds number. Also, linear stability analysis is used to understand the fluid dynamics observed. A set of partial differential equations governing the perturbed fluid flow are solved numerically and attempt is made to calculate the precise values of Reynolds number and blockage ratio at which different bifurcations in fluid flow are observed.

The problem of aerodynamics heating must be resolved to ensure safety of passengers with reduced drag for commercial feasibility of civil hypersonic fights. The aerothermodynamics of a conceptual blunt symmetric airfoil with a circulation enhancing flow through duct is investigated numerically with an unstructured Navier-Stokes Solver. The rectangular duct of slightly diverging cross sectional area makes the flow to enter into the airfoil from the lower surface near the leading edge and comes out of the airfoil at a point on the lower surface near the trailing, following a circular path. The travelling of air in a circular path increases the circulation about the airfoil and the leakage of high pressure air through the airfoil also decreases the pressure drag of the body resulting in high lift-to-drag ratio for the airfoil. The width of the flow-through duct housed inside an airfoil of 1 m chord, increases smoothly from 20 mm at the inlet to 30 mm at the exit. Two dimensional steady state solutions are obtained for a Mach 6 flow of air with static pressure and temperature of 16066 N/m2 and 216.65 K respectively. This paper discusses the feasibility of using a duct to enhance the aerodynamic efficiency of blunt airfoils at hypersonic speeds. The surface heat flux, aerodynamic drag and lift at various angles of attacks for a blunt airfoil with and without duct are presented in this paper.

The destabilization of a two-fluid interface is of interest in various applications ranging from spray formation to ocean-wave currents. In most practical spray systems, instabilities that occur on the interface lead to form fragments. Among such instabilities, those caused due to the radial motion of the interface in a cylindrical configuration (Rayleigh-Taylor) are of current interest. We study the instability characteristics of a cylindrical bubble surrounded by an infinite medium of liquid. Linear stability analysis is used as a tool to understand the mechanics. A general dispersion relation has been derived for an inviscid, immiscible and incompressible pair of fluids. This dispersion relation is used to predict the most unstable wavenumber as well as the dominant instability growth rate. It was found that the Bond number is a primary determinant of the most unstable wavenumbers, dominant instability growth rate as well as the neutral stability points. Surprisingly, it was also found out that radial velocity alone (in the absence of radial acceleration) is sufficient to destabilize a cylindrical interface, unlike in the case of either planar or spherical polar configurations.

In this work, a new set of generalized transport equations consistent with Onsager’s reciprocity principle are derived using moments based approach. The utilized distribution function can be expressed in terms of thermodynamic forces and their fluxes and satisfies the Boltzmann H-theorem. The derived equations are compared with Grad’s 13 moments equations for monatomic gas modeled as Maxwellian molecule. The merits of the proposed distribution function against Grad’s distribution function are discussed along with other advantages of our approach.

Flow visualisation experiments are reported on two-phase air-water flow through a 25 mm internal diameter, 8 m long horizontal pipeline in order to analyse the onset and evolution of slug flow over a wide range of superficial Reynolds number of liquid (Re_SL) and gas Reynolds number (Re_SG). The visualised images reveal that slug is formed when the amplitude of wavy interface increases over a stratified film and blocks the gas. As the slug passes the liquid level behind the slug significantly drops. Liquid level of this thin film is then observed to rebuild its level in a time whose order of magnitude is equal to the inverse of the slug frequency. Interfacial structures of slugs are analysed in terms of non-dimensional liquid height at five different axial locations along the test rig. Effect of inlet gas and liquid flow rates on the slug initiation and growth is also illustrated in terms of Re_SL and Re_SG.

This experimental study focuses on studying the flow characteristics of synthetic jet using inclined orifices. Synthetic jets with circular orifices of different inclination angles are studied quantitatively and qualitatively using Laser Doppler Velocimetry (LDV) and laser induced florescence (LIF, flow visualization) in quiescent flow environment. The flow from the inclined orifice is significantly complex than the flow from the normal axisymmetric orifice case. Fluid is ejected from the inclined orifice and rolls up into asymmetric vortex ring. It is observed that asymmetry in the roll-up of vortex rings at the orifice exit increases with increase of angle of inclination. Higher jet exit velocities are obtained for larger inclination angles as compared with equivalent normal synthetic jet.

The transverse jet injection into supersonic crossflow has additional complexities compared to the subsonic case due to the interaction of different shock structures with the oncoming boundary layer. The resulting flow field around the jet has many unsteady shock and flow features. In the current work, the mean and instantaneous flow fields around the jet are studied using Particle Image Velocimetry (PIV). The mean flow fields in the mid-plane show the jet expansion, Mach disk and shear layer between jet and crossflow besides the bow and separation shock. The effect of momentum flux ratio (J) on these flow features is studied. Instantaneous flow fields reveal the dynamics of jet, bow shock and the existence of large velocity fluctuations in the wake region.

Wind tunnel experiments are conducted on NACA 0012 airfoil model to investigate the effect of high reduced frequency and asymmetry in pitch oscillations on the aerodynamic characteristics and hysteresis behavior associated with the oscillating motion of the airfoil at Reynolds number 105. The aerodynamic loads are quantified by surface pressure measurements on the mid span of the airfoil. The results indicate that pitch asymmetry and high reduced frequency have profound effect on the flow structures, and hence the integrated loads on the airfoil section.

This chapter deals with the numerical simulation of the exhaust of an engine, passing through a pipe of 100 mm long and 30 mm diameter. The velocity and temperature profiles along with the concentration of exhaust gases are plotted along the axial length of the pipe. Further, a coaxial surface junction thermocouple (10 mm long and 3.25 mm diameter) is placed at an appropriate location of the pipe and the flow field is reinvestigated. In both the cases, the lateral variation of temperature and velocity, are found to be negligible. But, the composition of exhaust gas changes beyond an axial length of 20 mm which may be possibly due to chemical reaction of exhaust gases with ambient air. One of the important objectives of this simulation is to estimate a desired axial location of the thermocouple for a proposed experiment. Based on the simulated results, it found that the thermocouple can be mounted at any axial location between 0–20 mm from the inlet of exhaust pipe.

The micro-organisms and bacteria lead the decomposition/decay of moist potato. These failures are almost negligible when the moisture content of potato is reduced below 10 %. Convective drying effectively prevents those defects/failures in the food stuffs. An experimental facility is developed for convective drying of moist object. Time dependent mass of the rectangular potato is measured during drying and using this data the transient moisture content is estimated. Initial moisture content is estimated by a thermostatically controlled hot air oven. The drying air velocity is maintained 2, 4 and 6 m/s and it was experimented at different air temperatures of 40, 50, 60 and 70 °C. The equilibrium moisture content and equilibrium drying time (Fourier number) are found and tabulated. A correlation is developed for equilibrium moisture content and Fourier number based on the drying air velocity and temperature. Density of potato is estimated from the experimental data and a good agreement is noticed when compared with the data from literature.

The effect of Sodium pyrophosphate and polyethylene oxide on thermal diffusivity of Laponite RD colloidal suspension is studied with optical technique of Mach-Zehnder interferometer. Laponite RD is synthetic nano-crystalline colloid having a disk shaped monodispersed particle with radius 12.5 nm and edge thickness 1 nm. Aqueous Laponite suspension generally forms complex microstructure with and without addition of externally added salt. At low volume fraction and low concentration of externally added salt it forms dilute gel and at high concentration and high volume fractions, a disconnected Wigner glass. The appropriate concentrations of sodium pyrophosphate in the range of 5–25 mM and Polyethylene oxide (PEO) 0.5–1.5 wt% is mixed with 2–3 wt% Laponite RD suspension. The freshly prepared 10 days old Laponite RD suspension was stirred for half an hour before pouring in an octagonal test cell cavity. The top and bottom sides of octagonal cavity are attached to copper plates. Initially the suspension was kept at uniform temperature. Collimated laser light beam generated from He–Ne laser with 632.8 nm wavelengths is passed through the test cell in which Laponite suspension is kept. The initial alignment of the interferometer is in the infinite fringe setting mode, which is obtained by balancing the density of test cell filled with Laponite suspensions and reference cell filled with dextrose solution. Subsequently, there is step increase of temperature of top plate in the range of 1–3 °C. Refractive index variation through change in temperature of Laponite suspension leads to a well-defined interference pattern. The interferograms are then processed through fringe thinning procedure and are analyzed to obtain the time dependent temperature field varying with spacing of octagonal cavity. They are then compared with analytical solutions of the heat conduction diffusion equations. The comparison of least square fit of the experimental data with analytical solutions leads to estimation of thermal diffusivity. Interestingly even with very small concentration of sodium pyrophosphate, the Laponite RD suspension (around 2–3 wt%), shows a substantial reduction in thermal diffusivity values as compared to Laponite RD suspension. The aggregation rate of Laponite suspension as a function of pyrophosphate and polyethylene oxide concentrations are compared using static light scattering experiments from literature in order to interpret laser interferometric thermal diffusivity results.

Surge tank is provided in the secondary sodium circuit of Sodium cooled Fast Reactors (SFR) to protect the secondary sodium circuit components from the pressure surges due to sodium water reaction in Steam Generator (SG). The pressurized argon gas inside the surge tank above sodium will act as a cushion and absorb the pressure surges. The entrainment of argon gas into the sodium due to free level fluctuations, turbulence etc. can cause operational difficulties in reactor. It is necessary to develop effective gas entrainment mitigating devices which keeps the sodium free surface calm but the development only through experiments is difficult and time consuming. Therefore a CFD model of surge tank is developed to predict the surge tank hydraulics and it is validated through experiments. Velocity measurement in the model at different directions and different elevations has been carried out using Ultrasonic Velocity Profiler (UVP).

Synthetic jet is a train of vortex rings generated by repetitive ejection and suction of fluid through an orifice. One complete cycle comprises an ejection stroke followed by a suction stroke of diaphragm. The net mass flux is zero across the orifice exit but it imparts a positive momentum to surrounding fluid. The shear layer zone of ejected fluid rolls at the orifice exit and propagates downstream due to both, momentum supplied by forward stroke and the self-induced velocity of vortex ring. In last two decades, it has gain a significant interest in range of applications like combustion, heat transfer enhancement, propulsion & maneuvering, drag reduction, jet control and boundary layer control. This study is related to the formation and characteristics of synthetic jet in cross-flow. The synthetic jet used in the present study is circular and flush mounted with the curved surface of model. The torpedo shaped model has 60 mm diameter and is placed inside the horizontal and recirculating water tunnel with test section cross sectional area equal to 400 mm × 400 mm. At flow velocities 0.072 m/s, the behavior of synthetic is investigated at three different actuation frequencies 2, 4 and 6 Hz in the range of velocity ratio equal to 1.69–4.77. The bulk flow visualization using color dye is shown in two orthogonal planes (side and top view) parallel to the cross-stream flow direction. A two-component Laser Doppler Velocimetry (LDV) technique is used for velocity measurement of synthetic jet in cross flow.

High performance computing (HPC) facilities consist of a large number of computer servers, which dissipate thermal energy in a data center. Efficient heat dissipation of these high density servers is a major concern to increase the life of electronic devices. Cooling of these devices involve thermal management strategies based on energy efficient cooling in a raised floor configuration, which depends on proper air flow distribution in an under-floor plenum, configuration of perforated tiles and arrangement of servers in racks. The current investigation was carried out with an objective to study air flow pattern inside plenum and to find out a better predictive tile model for air flow distribution through perforated tile. The full scale Computational Fluid Dynamics (CFD) model was used to predict flow over perforated tiles and temperature distribution over server racks inlet at different cold aisles. The governing equations (mass, momentum and energy) were solved to compute flow and temperature distribution in the computational domain. The RANS based k–ε turbulence model was used for estimating turbulent kinetic energy (k) and turbulence dissipation rate (ε). The under-floor blockages and CRAC locations were found to be significant parameters influencing flow distribution in different cold aisles. The CFD model was validated by carrying out experimental works. The deviation in flow rates obtained by CFD model was within 15 % with respect to experimental values for different rows in cold aisle. Cold aisle containment for over provisioned case of data centre was studied using modified body force model, which predicted better hot air entrainment and momentum rise of cold air as compared to porous jump model. The root mean square error (RMSE) of the temperature predicted by the modified body force model was 1.68 °C, whereas the RMSE predicted by porous jump model was 1.72 °C. Based on the CFD simulation studies, some energy saving opportunities were suggested for improving the thermal performance of the HPC facility.

The two-dimensional numerical simulations of Newtonian fluid stream about a square bluff body have been studied in an unconfined configuration in addition in the propinquity of a plane wall. The comparison of flow and heat transfer constraints is done with the pure unconfined flow about a square obstacle. The set of physical constraints considered as Reynolds numbers (Re) = 100, 120 and Prandtl number (Pr) = 0.7 (air) at varying values of gap ratios (g). The values of drag and lift coefficients, and average Nusselt number are computed. The present study shows that on increasing the gap ratio, the drag coefficient is acquired to be the highest for the gap ratio of unity and it is observed the lowest for the unconfined case. Lift coefficient decreases and average Nusselt number increases with increasing gap ratio, but opposite effects are observed for the unconfined case. The flow becomes steady at low gap ratio, but on increasing gap ratio the flow behavior changes to periodic unsteady. The augmentation in heat transfer is found about 35 % for g = 1, with respect to the corresponding value for the unconfined case.

A finite volume adaptive mesh redistribution method for efficient and accurate simulation of one and two dimensional compressible Euler equations is developed. The method consists of two coupled steps; evolution of the governing equations using an adaptively redistributed mesh followed by a redistribution of the computational nodes. Mesh redistribution is accomplished through the solution of an elliptic equation which allows for determination of redistributed coordinates corresponding to the physical domain on a simplified computational domain, discretized using a uniform Cartesian grid. The governing hyperbolic compressible Euler equations, originally defined in the physical domain, are first transformed on to the simplified computational domain and then recast in a strong conservative form. These are then solved directly on the computational domain with the primary aim of maximizing accuracy while minimizing the computational overheads associated with the grid redistribution. The method is demonstrated on compressible Rayleigh-Taylor instability in two dimensions.

Reverse flow in a parallel walled test channel placed in a wider channel is observed when an obstruction is placed at the test channel entry. When the position of the obstruction at the test channel entry is varied relative to the test channel, the flow inside the test channel reverses (opposite to the wider channel flow), stagnates or flows in the forward direction. The present study is to establish this unsteady flow, involving reverse flow in the converging channels for various g/w ratios at Re = 4000. The converging angles studied are 0.2°, 0.4°, 0.6°, 0.8° and 1.0°. The reverse flow magnitude increases as the convergence angle is increased till 0.6°, and then starts decreases when the convergence angle is further increased. The results also show us more insight about the reverse flow phenomenon and mechanism of fluid pumping due to shear layer interaction at channel exit for the various convergence angles.

A unique hybrid Aerodynamic Shape Optimization (ASO) framework is devised for axisymmetric bodies with minimum drag coefficient in hypersonic inviscid flow at zero angle of attack. The hybrid ASO framework that has been developed in this paper makes use of a combination of low fidelity framework and high fidelity framework, with the intention to reduce the turn-around time from initial guess to final optimal solution with accurate estimation of cost function. This was achieved when low fidelity framework was able to generate near optimal solution with quick and reasonably accurate estimation of coefficient of drag (cost function for present study). The near optimal solution was then fed as the initial guess for high fidelity framework and it accelerated the convergence to global optimal solution. The low fidelity framework comprised of Modified Newtonian Theory as flow solver while ANSYS FLUENT (v 14.5) formed the flow solver for high fidelity framework. Optimization was effected using Steepest Decent in both the framework and Bezier curves were used for generic shape representation of bodies. ICEM-CFD was used to create the structured grid as required in Fluent. The result show significant reduction in computational cost from initial guess to final optimal solution. It was also observed that the optimal solution obtained from proposed multi-fidelity framework and optimal solution from CFD simulation only, are nearly comparable with marginal difference in the volume. The optimization also resulted in a reduction of coefficient of drag by more than 28 %.

Present numerical study aims at suppression of vortex shedding formed over a circular cylinder using different combinations of slot and control plates. Unsteady, two–dimensional computations are carried out for laminar, isothermal conditions at a Reynolds number (Re) of 150 using commercially available CFD software ANSYS-FluentTM. Numerical simulations with different passive controlling methods have been carried out to reduce the vortex shedding frequency or to suppress it completely by using the configurations, such as cylinder with control plates, and cylinder with combinations of slots and control plates. By carefully comparing the numerical results of all the cases, it is found that cylinder with control plates at 5° angle is the best case where the vortex shedding is completely suppressed which in turn reduces the drag force significantly. However, in other cases, it was partially suppressed but increases the drag force due to vortex formed near to the control plates or not having any effect on vortex shedding. The results are presented in terms of vorticity and streamline contours, C_l, C_d and Strouhal number.

Spurious pressure fluctuation and poor mass conservation are considered as the limitations of immersed boundary method (IBM). Over last decade, various implementations are developed to overcome these issues, which are usually mathematically involved and computationally expensive. In this paper, a simple and robust methodology has been proposed with good mass conservation property that results in smooth pressure fluctuations over moving surfaces. A simple quadratic interpolation/extrapolation scheme is used for reconstruction of solution at immersed and ghost nodes in. The proposed scheme has been implemented for fixed and moving three-dimensional boundaries and validated with available literature data. Overall second-order accuracy has been maintained. The achieved results show a second order accurate mass conservation. Spurious pressure fluctuations are also observed to disappear with mesh refinement.

This work is focused on the estimation of power requirements of an electric vehicle platform (EVP) for intra-campus transport using high fidelity computational fluid dynamics (CFD) model based on the incompressible Navier-Stokes equations. The starting point is the ordinary auto rickshaw in which a battery powered electric motor replaces the IC Engine. The work aims to benchmark the aerodynamic drag of the EVP against the standard auto-rickshaw and for designing the chassis and to assess the power requirements of the EVP.

Matrix dissipation scheme is known to give more accurate solutions than scalar dissipation scheme. Matrix dissipation scheme was implemented in in-house developed JUMBO code (block structured vertex based finite volume RANS solver), which currently uses scalar dissipation scheme to introduce artificial viscosity. The implemented matrix dissipation scheme was tested for transonic flow over various airfoil sections. Numerical solutions obtained using matrix dissipation model were found to be more accurate than scalar dissipation model, particularly in the neighborhood of shock waves while still maintaining good convergence properties.

The problem of pulsating flow through a circular pipe was analyzed numerically in the laminar flow region with the flow at the pipe inlet consisting of a fixed part and a pulsating component varying sinusoidally in time. The pipe wall was kept at an uniform temperature. The solution of two dimensional Navier-Stokes equations was obtained using Ansys Fluent software code and user defined function. The effect of Reynolds number, Strouhal number, and amplitude ratio is studied for 200 ≤ Re ≤ 2000, at 2 ≤ St ≤ 20 and 0.1 ≤ A/D ≤ 1. It is noticed that the large amplitude ratio combined with flow reversal occurring in a small zone near the wall promote augmentation of convective heat transfer. Small hike in Nusselt number is noticed with increase in Re and St; however, it changes substantially with hike in amplitude ratio.

A comprehensive investigation on mixed convection in a ventilated enclosure has been carried out numerically for different positions of heat sources at the sidewalls. The relative position of the isothermal heat source and heat sink on both vertical walls influences the heat transfer process. Different configurations are simulated using an in-house developed CFD code, based on finite volume method. The characteristics of heat transfer, flow complexity and entropy generation are calculated as a function of Richardson number (Ri = 0.01–100) and Reynolds number (Re = 100). The results for different position of heat sources and heat sinks are presented along with isotherms, streamlines and Bejan number. The results show that the performance with middle-middle position of heat source is always superior.

In pulse jet filter bags, the pressurized air is discharged from the air reservoir into the filter bag via the diaphragm valve and blow pipe. The cleaning of the filter bag depends on the flow properties like pressure, velocity and mass flow rate of the air at the exit of the holes. The properties at the exit of the holes in a blow pipe, like the pressure, angle of inclination and mass flow rate, are studied numerically by analyzing a three dimensional model of the blow pipe. The experimental values of pressure at the exit of the fourth hole are used to validate the model. It is seen that the mass flow rates at the exit of the holes are not uniform. Also angle of exit air pulse from orifice is not coaxial to the axis of the orifice.

Forced convection heat transfer from an inclined elliptical cylinder at constant heat flux has been investigated numerically in the steady flow regime. The detailed structure of flow and heat transfer characteristics around an elliptical cylinder with minor to major axis ratio 1:2 have been examined over a range of Reynolds number (1 ≤ Re ≤ 30), Prandtl number (1 ≤ Pr ≤ 100) and angle of inclination (0° ≤ λ ≤ 90°). Extensive results are obtained for the velocity and temperature fields in terms of streamline and isotherm patterns in the proximity of the cylinder. Evidently, the orientation of the elliptical cylinder strongly influences the flow patterns around the elliptical cylinder and the onset of flow separation. The dependence of the average Nusselt number on the Reynolds number and Prandtl number has also been studied over this range of inclination.

A detailed numerical study has been carried out for the steady, two-dimensional, laminar natural convection heat transfer from two heated cylinders (equal temperature and radius) immersed in a Newtonian fluid inside a cold square enclosure. The coupled governing differential equations (continuity, momentum and energy) have been solved over the ranges of dimensionless parameters as follows: Grashof number, 102 ≤ Gr ≤ 104 and Prandtl number, 0.7 ≤ Pr ≤ 100. Detailed structure of the flow and temperature fields are presented in terms of the streamlines and isotherm patterns which help delineate the regions of high/low temperatures and general flow characteristics respectively. At the next level, the heat transfer characteristics are presented in terms of the local and average Nusselt number. The dependence of the Nusselt number on the both Grashof and Prandtl numbers is analyzed and it shows a positive dependence on both of the dimensionless parameters, namely, Grashof (Gr) and Prandtl (Pr) number.

A nozzle is a variable cross sectional area used to accelerate the flow. As the fluid flows through the nozzle, the kinetic energy of the fluid is increased at the expense of pressure energy. The main use of nozzle is to produce a jet of steam (or gas) of high velocity to produce thrust for the propulsion of rocket motors and jet engines and to drive steam or gas turbines. Nozzle has many applications in industry of turbo machinery, separation systems, the jet propulsion units, geo-environmental techniques, air conditioning, thermal ejectors, wind tunnels and many others. The present work incorporates the detail study about subsonic and supersonic nozzles. The concept of method of characteristics is used in designing of nozzle. The program is developed in the language C++, which generates the profile of both the subsonic and supersonic nozzle. To study the performance and characteristics of the nozzles, the experimentation is carried out at different back pressures. These experimental results are compared with the theoretical, isentropic one dimensional flow for variable area passages. The geometry of the nozzle is created in modeling software GAMBIT 2.4.6 and the numerical simulation is carried out in FLUENT 6.3.26. The numerical results are compared with experimental results at design and off-design conditions. The results indicate that, there is good agreement between the graph of experimental and numerical results. In both the analysis at design condition, the flow gets accelerated throughout the nozzle length. At the design condition, the phenomenon of flow through the nozzle is changed with variation in back pressure value. For very high value of back pressure, compared to design pressure, the convergent part of the nozzle accelerate the flow and the divergent part of the nozzle act as a diffuser and decelerate the flow. On further reduction in the back pressure, the shock phenomenon is observed in the divergent portion of the nozzle. This shock position shifts downward from the throat to exit of the nozzle, with the reduction of back pressure.

The current fin industries are working with a prime goal to reduce the overall dimensions of the fins with enhancement of the heat transfer rate per unit weight of the fins. To meet the industrial demands it has become mandatory to optimize the shape and the size of the conventional fin systems. Introduction of an extended surface on a heated plate does not always ensures increased rate of heat transfer to the surroundings. An effective utilization of the wetted surface area is major factor in this perspective. Use of fins with different configurations of holes, over a heated surface is found to have very less effect on the average convective heat flux. However, with the considered system of holes, the weight of the fins can be hugely reduced without much lowering of the outlet convective heat flux. With air as the working fluid, a 3-D system of aluminum fins has been numerically modeled in the present work, simulating a conduction-convection scenario.

Variable density flows are basically those in which density variations cannot be neglected and hence the density is treated as a variable. This formidable change in density may be caused by either of three variables of the ideal gas equation (when dealing with gases) namely pressure, temperature and molar-mass. When pressure causes considerable change in density, the flow is no longer incompressible and they are dealt separately under compressible flows. But when density variation is caused by the other two aforementioned variables then the flow is still incompressible but the density will vary. Presence of varying density in governing equations poses a formidable challenge for numerical simulation as there is a very strong coupling between momentum and scalar transport equations. This work involves the development of three-dimensional Navier-Stokes solver to compute variable density incompressible flows on hybrid unstructured grids. The density variation due to temperature and species concentration has been considered.

Solidification and melting problems are phase change kind of problems in which interface moves and it separates the phases. Natural convection and conduction are the main mechanism behind the physics of these problems. In the present study, Navier-Stokes equations along with continuity and energy equation are solved to predict the phase change pattern of pure metals (e.g. Gallium) and alloys (e.g. Steel). Here, enthalpy method is used to find the temperature distribution and to track the position of the solid-liquid interface with time. A coupled fully implicit method is used to solve the momentum and energy equation. Both isothermal and mushy region phase change problem is presented and verified with numerical results available in the literature.

A fundamental study to investigate the effect of pulsatile flow past square cylinder at Reynolds Number, Re = 100 and Prandtl Number, Pr = 0.7 has been performed. The flow pattern is represented by three different non-dimensional parameters: the Richardson number (Ri), amplitude (A) of the incoming pulsatile flow velocity, and Keulegan-Carpenter number (Kc = V_o/Lω). The equations solved are Navier–Stokes and energy equation to compute the dynamic flow field. The numerical simulations are implemented by using commercial a finite volume solver. The parameters varied are Ri, (0, 0.1 and 0.25), A (0.2, 0.4 and 0.6) while Kc is kept fixed at 0.5. The effect of pulsatile flow is studied and results are compared with previous numerical results for uniform flow. It is found that for the case of Pulsatile flow vortex shedding continues even for Ri = 0.25. Also the number of Vortices formed and the distance traveled by said vortices is determined by the oscillating wave amplitude .

The all-vanadium redox flow battery has been accounted as one of the viable rechargeable batteries for large scale energy storage devices that can be united with renewable energy sources such as wind and solar energy for electrical energy distribution and storage. The main advantage of the all-vanadium redox flow battery is capable to withstand average loads, higher power output and higher energy efficiency. The battery shows good unsteady behavior and sustains a sudden voltage drop. A transient, isothermal, three-dimensional model of the all-vanadium redox flow battery is developed, which is governed by the conservation laws, such as momentum, mass and charge, united with a kinetic model for reaction having vanadium species. In this context earlier efforts reported in the literature were mainly focused on simulation of the variation of the charge/discharge characteristics of the cell. There is a need to optimize the cell parameters so as to improve cell performance. The performance of the battery is also studied numerically with the three dimensional isothermal unsteady model. This model is employed to predict the effects of change in concentration, electrolyte flow rate and electrode porosity.

A generalised three-dimensional solver based on unstructured grid methodology has been developed for electrohydrodynamic flows. The Navier-Stokes equations with electrical field source term are solved in conjunction with the coupled electrical potential and ion charge density equations in a finite volume framework. An iterative boundary condition for updating the value of charge density on the discharge electrode is used while solving the electrical field equations. The solver is validated with available literature and the good agreement is found.

The paper discusses the combined implementation of overset grid and patched grid methodologies and it’s testing for transonic and supersonic flows. The motivation is to make the grid generation process easier and less time consuming as well as having optimum resolution as per the requirement of local flow gradients, with no effect on the accuracy of simulation. In the near-body region body fitted curvilinear structured grid and in the off-body region Cartesian grid layers with gradual coarser resolution away from the body were used. Curvilinear and Cartesian blocks were coupled with overset grid technique, where as different Cartesian layers were coupled through grid patching. In the overset grid module, barycentric coordinates were used to search the donor cells of each fringe cell. Area weighted averaging was utilised for fringe cell conservative variable interpolation from their corresponding donor cells and it preserved the conservation at shocks without generating spurious oscillations. The area fractions required for area weighted averaging were found by using polygon clipping algorithm in efficient manner. Steady state inviscid & viscous flows and unsteady state moving shock simulations were carried out to test with patched grid and overset grid combination and shocks passed through these block boundaries without getting distorted.

Jets of gas mixture are an important part of molecular beam extraction studies and plasma studies. Strongly underexpanded supersonic free jet issued from a nozzle is analyzed numerically using commercial CFD software FLUENT. The straight contoured converging type of nozzle is used with length to throat diameter ratio of 2:1 and throat diameter 50 micron. The Argon and Nitrogen gas mixture is used as working fluid with 0.5 mass fraction of argon and nitrogen each. The inlet to outlet pressure ratio changes from 15 to 40. Shock dimensions and locations agreed with empirical relations derived from previous experimental work. The present work fundamentally focuses on zone of silence (ZoS) (isentropic, inviscid, supersonic region inside the strongly under-expanded jet). It focuses on examining effect of flow properties in reservoir and background on onset of supersonic jet and ZoS characteristics, rate of variation of flow variables inside supersonic jet ZoS.

Three dimensional CFD study is done here—using a commercial software- to propose an efficient PCHE (Printed Circuit Heat Exchanger) model; used as a recuperator in International Thermonuclear Experimental Reactor (ITER). The present work is aimed to study a wavy channel based PCHE model, with certain modifications in design to demonstrate better thermal and hydraulic performance. The waviness for the hot as compared to cold channel is in anti-phase. The study is done for various angle of bend (0° (straight), 5°, 10° and 15°) and Reynolds number (350, 700, 1400 and 2100). The inlet temperature of the hot and cold channel is taken as 1173 and 813 K, respectively; and the operating pressure of the PCHE is taken as 3 MPa. Thermal hydraulic performance parameters are presented for the various periodic sections of the wavy-channel. Power density as well as pressure drop increases with increasing Reynolds number and angle of bend. Wavy as compared to plane channel based PCHE is demonstrated here to give better thermal-hydraulic performance.

Printed Circuit Heat Exchanger (PCHE) is a plate type compact heat exchanger that usually finds application in high pressure systems. The scope of the present work is restricted to two high pressure applications, viz. (i) Test Blanket Module (TBM) cooling circuit in International Thermonuclear Experimental Reactor (ITER) and (ii) Intermediate Heat exchangers (IHX) in Very High Temperature Reactors (VHTR). A counter flow PCHE, made of Alloy-617, working in He–He circuit has been considered as the reference for numerical simulations performed on ANSYS Fluent 13. A reduced model for single banked straight channel PCHE model has been proposed and is validated with literature [1]. The scientific and engineering aspects of flow and heat transfer characteristics in straight channel PCHE have been carefully examined for constant as well as varying thermo-physical properties and are compared with each other. Three different channel configurations viz. zigzag, sinusoidal and swept-zigzag (trapezoidal) have been numerically modeled and tested in a single banked PCHE core and the respective thermo-hydraulic performances are compared with straight channel PCHEs.

The flame deflector of a rocket engine test facility needs to be protected from the high thermal loads resulting from the impingement of high velocity and high temperature exhaust flame on it during the hot test. The flame deflector is cooled by water injected from holes in the deflector plate. In this paper ANSYS Fluent was used to analyze the flow over the flame deflector. The engine plume structure and its impingement characteristics on the flame deflector were determined in the absence and presence of water injection. The water injection pattern was optimized for the better cooling of the deflector plate. SST k-ω model was used for the turbulence modelling. Discrete Phase Model was used to simulate water injection from holes provided in the impingement plate.

Numerical and experimental study has been carried out for a three-dimensional wall jet developing on a concave curved surface. A square orifice is used to generate the free jet. The flow characteristics such as mean velocity profiles, decay of maximum velocity, half width growth and variation of curvature parameter are presented in this paper. For comparison purposes, measurements are also taken on plane surface. The mean velocity profiles show similarity for both the surfaces and no effect of curvature is felt. It is observed that maximum velocity decay is slower on concave surface when compared to the decay rate over plane surface. The half width growth is decreased over concave surface.

Low speed wind tunnel (LSWT) is a device, generating uniform airflow relative to a model of the body that measures aerodynamic force and pressure distribution to simulate with actual conditions. This paper will lay emphasis on the procedure adopted in the design of a tunnel (open circuit blow down type) along with the detailed analysis of flow through it and forces generated on an airfoil NACA 4412 with the help of CFD based software Fluent 6.3. In purview of the designing and testing economics, it is not feasible to go for the real time simulation at original facilities. So, we have decided to make this small scale LSWT as forces and pressures developed by the model can be applied to the prototype by multiplying the force co-efficient obtained in the computational analysis of the model with the factor ½ ρ _∞v_∞2 A_P having values of parameters in the factor corresponding to full scale.

Flame spread over an array of fuel sheets of finite width size has been modeled and numerically investigated for opposed, low convective flows in microgravity. As opposed to the previous studies based on 2D models, steady flame spread rates were observed for all separation distances up to the separation distance of flame extinction. The flame spread rate increased with decrease in separation distance up to a point where it was maximum, further reduction in separation distance, reduced the flame spread rate. The flammability map as a function of separation distance was also obtained for different fuel widths. While the extinction map qualitatively matches with the flammability map obtained from the 2D model, the flame extinguished at higher oxygen levels with the decrease in fuel width due to radiation heat losses.

The problem of cavity flow concerning mixed convection fluid flow and heat transfer phenomenon is less pursued in lattice Boltzmann methods compared to other conventional numerical techniques. The objective of this present work is to study mixed convection flow in a differentially heated lid–driven square cavity filled with low Prandtl number (Pr) fluid such as, air (Pr = 0.71) with varying Richardson number (Ri) between 0.01 and 100 by using thermal lattice Boltzmann method in the incompressible limit. In order to discuss the effect of both aiding and opposing mechanisms of mixed convection, two different sets of velocity boundary conditions at the two vertical lids are considered. A comparison is carried out for those cases which have existing results computed through other numerical methods and good agreement has been found.

We propose an unified formulation for thermobuoyant flows an arbitrary mesh topologies. Unlike incompressible flow, the pressure correction equation is derived from the energy equation. The resulting Poisson’s equation reduces to continuity constraint $$ \nabla \cdot \varvec{u} = 0 $$∇·u=0, only in absence of thermal gradient and compressibility effects. Investigations are carried out for flows with small and large temperature differences in a differentially heated square enclosure. Studies using Cartesian and triangular grids show that the proposed approach can successfully simulate non-Boussinesq convection with extreme density variation.

A fire dynamics simulator (FDS) code, based on large eddy simulation (LES) technique, has been used for simulation studies of smoke spread due to fire in a multi-storied building. The existing natural ventilation system is found to be inefficient in smoke extraction. To safeguard the stairs from smoke accumulation, various methodologies of mechanical ventilation have been adopted to analyze the situation. Suggestions on improving the safety of the building have been provided and their feasibilities have been discussed.

This paper presents the results from numerical simulation of jet flow emanating from a cruciform orifice. OpenFOAM is used for the simulations with RANS standard k-ε turbulence model. The results are validated with the experimental data of Quinn [1]. Mean flow quantities and turbulent quantities are discussed in detail. The evolution of cruciform shape to circular shape is described with various contours of mean flow and turbulent quantities. Possible reasons for the evolution of cross sectional shapes are discussed.

Experimental analysis of turbulent flow properties associated with early entrance regime of rectangular duct flow is reported. Deterministic and statistical properties are measured across the width and depth of the rectangular duct at different locations along the duct. Measurements are carried out using hot film anemometer. Experiments are performed for Reynolds number in the range of 35000–115000. Turbulent time scale is obtained using autocorrelation function which leads to determination of integral and Kolmogorov length scale at various flow conditions. Variation of normalized centerline velocity (U_e/U_b) along the duct for different Reynolds number in the range mentioned above is analyzed. FFT analysis is carried out to detect the power content of flow and also to depict the chaotic nature of the flow.

We evaluate the performance of the newly developed analytical gas kinetic method (AGKM) by Xuan and Xu [10] to fully three-dimensional turbulent flows by simulating decaying compressible turbulence. Evaluation is performed in low, intermediate and high Mach number regimes. We find that in the low and the intermediate Mach number regimes, AGKM results shows excellent agreement with high order accurate results obtained with traditional Navier-Stokes solvers in terms of turbulent kinetic energy decay and pressure/density fluctuations. However at high Mach numbers (>0.7), the performance of AGKM is inadequate and may require enhancement such as weighted essentially non-oscillatory schemes (WENO).

The flow prediction using computational fluid dynamics (CFD) in a given flow geometry becomes a complex issue when the flow is in the transition region. The motivation for this study is to find the best turbulence model for prediction of air flow in the air gap of helmet. In CFD if the flow for a given geometry is known to be turbulent then any standard turbulence model such as the k–ε model does a reasonable job of predicting the mean flow quantities. As a first step this study aims to find the optimum turbulence model for near transition flows for pipe flow problem which is a benchmark flow problem. Using simple flow problems such as pipe flow we show that even in this simple case if the flow is laminar and a turbulence model is used in the CFD simulations, the results with most turbulence models are erroneous. For a model to perform well under a laminar condition, it should predict a laminar flow and nearly zero eddy viscosity. Results of CFD simulations for pipe flows indicate that Spalart Allmaras (S-A) model shows these trends. Its relevance to helmet is because when we carry out CFD simulations for a helmet the air flow domain is large and almost all of it includes the region outside the helmet, where the flow is known to be turbulent. The boundary conditions are set on this outer domain. The gap between the helmet and the head of rider is very small and it is not a standard geometry. Since we do not know the velocities at the inlet of this thin air gap, we do not know a priori if the flow is in turbulent or laminar or in the transition region in the air gap. So it becomes imperative to work with a turbulence model that will perform well in laminar as well as turbulent flow conditions. The numerical experiment on simple pipe flow shows that S-A model performs better than the standard two equation models when the flow is in the laminar or transition regime and performs almost the same as the other two equation models in the turbulent regime. Having established this, we then try to match the results of the S-A model with experimental results of flow in 3-dimensional head-helmet arrangement and found that for 3-dimensional flows the S-A model does a better job than the k–ε models. S-A Model is then used to predict the best arrangement of vents for improving ventilation in helmet. It is found that ventilation in helmet with central and side vent is better than helmet with only central vent or side vent.

This study focuses on evaluating the heat transfer augmentation and pressure losses in a stationary two-pass square duct with thermally active rib turbulators. Two different rib arrangements (90° and 60°-V) were investigated with a fixed blockage ratio (e/D _h ) is 0.125 and the rib pitch-to-height ratio (P/e) is 10. The stainless steel foil is used as heater which practically ensures uniform heat flux boundary condition. Infra-red thermography (IR) technique has been employed to obtain the surface thermal maps and local Nusselt number distribution for three different Reynolds numbers namely, 20,000, 30,000, and 40,000. In addition, the effect of pitch has also been studied by using two pitch ratios namely, 10 and 20 for the same rib angle of 60°-V. The results reveal that the 60°-V shaped rib arrangement provides a higher thermal performance than the 90° ribs. 60°-V rib arrangement with higher pitch ratio shows poor performance compared to the lower pitch ratio cases.

The pressure Hessian tensor plays a crucial role on the dynamics of velocity gradient tensor. Therefore, understanding the evolution mechanism of pressure Hessian in compressible turbulence is of much interest. Using the results of direct numerical simulation (DNS) of compressible decaying isotropic turbulence, we present the complete budget of pressure Hessian evolution equation. The relative significance of various mechanisms responsible for pressure Hessian evolution is closely examined. This study is expected to directly contribute toward the development of improved closure models for the Lagrangian stochastic method.

The effect of sidewall in self-sustained oscillation of an open cavity has been analyzed to understand the flow instability and influence of acoustic waves for transonic flow using Large-Eddy Simulation (LES). The present simulation resolves the formation of shear layer, its rollup resulting in large-scale structures apart from shock-shear layer interactions and evolution of acoustic waves. Presence of sidewall generates streamwise vortices that grow and convect downstream, while interacting with the spanwise rollup of shear layer. This results in coherent structures that finally impinge on the aft wall generating acoustics.

In the present work, numerical study of a gas-solid flow inside reverse flow type of cyclones are carried out using Euler-Lagrange approach. All numerical simulations are carried out using ANSYS FLUENT having the same performance parameters. Reynolds Stress Model and Large Eddy Simulation are applied for fluid flow simulation, hence solid particles are simulated using Discrete Phase Model. The objective is to study the effect of the geometrical parameters on cyclone performance and to optimize the significant geometrical parameters. For that, the study of each single parameter like vortex finder diameter, cone length, vortex finder length, barrel height and con-tip diameter is done separately that is having different ranges for each parameter. The final optimum design having optimum pressure drop and optimum collection efficiency is identified from performance curves of individual parameters. A comparison of numerical simulation of the optimum new design and the Stairmand High-Efficiency design shows particle collection efficiency and total pressure drop has significantly improved on the new proposed design compared to the Stairmand High-Efficiency design.

Buoyancy affected turbulent flow in a channel is numerically simulated via LES, subjected to large temperature gradient. Temperature dependent fluid properties like viscosity (µ) and thermal conductivity (κ) considered as variable as Boussinesq assumption fails to capture the insight physics. With increased stratification, turbulent momentum and buoyancy fluxes decreased at an alarming rate in the core of the channel due to the formation of some wave like structures (IGW). The most striking feature produced by the temperature dependence of viscosity is flow relaminarization on the hot side of the channel (where viscosity is higher) and movement of IGW from core to hot side. Pronounced modifications in turbulent structure are observed qualitatively and quantitatively, and the deviation in the behavior is due to the non-Boussinesq assumption.

The present work proposes a design methodology to achieve a desired single phase flow distribution in a T-junction. The desired flow control is achieved by contouring the flow path of the duct using three bi-quadratic Bézier curves. A Bézier curve is one of the parametric curves which is defined by a set of a few control points. These curves possess some interesting properties which render them as a good choice for the representation of smooth curves. A bi-quadratic Bézier curve is defined by five control points of which four are fixed in the present work (two control points to mark initial and final positions and another two points adjacent to them for tangent continuity). Different curves, which are nothing but the contours depicting the flow path, are obtained by moving the remaining one control point for each curve. Since in two-dimensional simulation, each control point is defined by two coordinates, in total, there are six optimization design variables for the three Bézier curves. The present work determines the optimal values of these design variables using CFD based optimization. The optimization is carried out using Box’s complex method with the objective function being the minimization of the percentage absolute error in the flow rate in the branch outlet. Constraint surfaces for the design variables are described such that the Bézier curves do not intersect each other. Numerical simulation of the geometry yields the value of objective function. The geometry creation and numerical simulation are performed in GAMBIT and FLUENT respectively in batch mode by integrating MATLAB, GAMBIT and FLUENT to enable automated optimization. Two dimensional numerical simulations were performed on a T-junction for three cases with branch outlet flow rates of 30, 50 and 70 % of the incoming flow rates. The optimal geometry for all the studied cases is determined within an flow rate error of 3 %.

In this chapter an experimental and numerical simulation were carried out for diesel spray to investigate its characteristics over a wide range of pressure. It would be helpful to predict the spray behavior such as penetration length, atomization, droplet distribution and spray angle for different pressure differences, covering low to high injection pressure. By knowing the behavior of injector over a pressure range gives a way to discover its applicability in a particular engine. The effect of various spray breakup models is studied and its influencing parameters like breakup length, breakup size constants were optimized iteratively. These parameters have a great influence in deciding the way in which the primary and secondary breakup occurring. Grid independency is done to have an optimized grid size by making a trade-off between accuracy and simulation time. Also the effect of discrete phase models (DPM), turbulence models and its constants, total parcels and maximum cells used for adaptive meshing were studied and compared with the test bench results. From the numerical simulation results, the optimum parameters were decided to predict the spray behavior closer to the test bench results.

This study reports on the investigation of flow structures in a slotted wall-jet using both Detached Eddy Simulation methodology in conjunction with Proper Orthogonal Decomposition (POD). The investigated Reynolds number of the wall jet based on the slot height is Re = 2500, while the transient behaviour of the jet is studied for different flow times. It is found that the simulated data compare well with the experimental data. Since the flow is unsteady, it is expected that there will exist numerous unsteady events. We, therefore, use proper orthogonal decomposition (POD) to identify coherent structures in this transient flow. Behaviour of the mode shape at different flow time is also discussed and reported.

Two-phase flow in multiple horizontal heated channels has wide applications in heat exchangers, solar heating systems, nuclear systems etc. The theoretical study of the two-phase flow instability analysis for parallel channel was carried by Zhang et al. [1]. This was done for vertical channels and they used nodal method to analyze stability of the system. Similar analysis was done by Lee et al. [2, 3] and Nayak and Vijayan [10], for multiple, vertical boiling channels with forced flows. Following the Zhang et al. [1] and Lee et al. [2, 3], the stability analysis of multiple horizontal channels with uniform heat flux has been carried out. The system is mathematically represented by non-linear PDEs using mass, momentum and energy equations in single as well as two-phase regions. Coupling equation is being used under the assumption that pressure drop in each channel is same and the total mass flow rate is equal to sum of individual mass flow rates. The homogeneous equilibrium model is assumed to be valid in the two phase region. Stability boundary is obtained in terms of phase change number (N _pch ) and Sub-cooling Number (N _sb ) and is validated by comparing it with result obtained by MatCont using the same parametric values. Numerical simulation of the time-dependent, nonlinear ODEs are carried out for selected points in the operating parameter space to obtain the actual damped and growing oscillations in terms of the channel inlet velocity which verifies the stability behavior across the stability map.

The study of mixing dynamics in stratified environment is very important as it has wide applications ranging from oceanic and atmospheric circulation to astrophysical and engineering flows. The stratification refers to density or temperature variation along height. Here, the entrainment dynamics of vertical turbulent buoyant jet/plume into a linearly stratified medium for varying Brunt Vaisala frequency (N) is presented by analyzing the development of large-scale and small-scale flow patterns. The experimental facility for this study consists of two square acrylic tanks. One of them is the stratification tank, which is linearly stratified (∂ρ/∂z < 0) with the help of water and commercial salt. The second tank is the reservoir tank that is filled with water. The fresh water is injected into the stratified tank to study the plume dynamics. The ensuing evolution of buoyant jet is studied using high-resolution camera and commercial dye, and bulk flow parameters are obtained. The experiments were carried out to the study the wall effects on the buoyant jet characteristics. The first set of experiments were conducted in the rectangular tank having a larger aspect ratio, a = 4, where aspect ratio is defined as the ratio of length (L) to width (W). The second tank has an aspect ratio of approximately a = 1. Mixing characteristics such as spreading height of plume, maximum height of plume and radial intrusion of plume were measured and compared. The results indicate that the presence of wall does change the mixing behavior of the jet when compared to the unbounded wall case.

Features like high power to weight ratio, self lubrication, heat dissipation and fast control make hydraulic systems superior to mechanical and electric systems. Such systems are used in aircraft, motion simulators, metal-cutting, universal-testing machines and material handling for heavy industries. For a precision operation, it is usual to employ electrohydraulic servo systems that are more sophisticated than systems with proportional valve. Due to larger deadband and higher flow nonlinearities, the low-cost rugged proportional valves together with standard PID controllers result in poor response for tracking demand. A controller has been designed through a novel state estimation algorithm and the usual pole placement (PP) technique by carefully choosing the operating points. One high friction cylinder and another industrial grade cylinder have been driven separately by using the same proportional control valve. The designed controller has yielded better performance compare to the PID controller.

The runner of turbine extracts energy from flowing water and hence plays great role in efficiency of turbine. The design of runner is based on many assumptions as the flow behavior is affected by many design parameters. Hence it is customary to assess the flow behavior in runner space for its efficient design. In this paper, numerical simulation of Francis turbine space has been carried out for four variants of runner with different blade stagger values at three guide vane openings. The local and global hydrodynamic parameters for runner and turbine are computed and the effect of stagger on these parameters at different turbine operating regime is studied.

Rib turbulators are extensively studied turbulence promoters employed in numerous industrial applications such as cooling of gas turbine blades and different electronic components, nuclear reactors and compact heat exchangers etc. for heat transfer augmentation. Some of the recent studies have shown the effect of altering rib profiles other than the square along with the effect of slit within it at fixed ratio of rib pitch to height (p/e). The present investigation focuses to explore the effects of p/e (p/e = 6, 8, 10, 12) on heat transfer augmentation and pressure penalty. Liquid crystal thermography (LCT) was applied to measure surface temperature distribution with temporal variation and ultimately the local heat transfer coefficients. Transient experiments have been conducted in an open-circuit, suction type air flow system at Reynolds number (Re) ranging from 9400 to 58850 (based on hydraulic diameter of the test section) and at a fixed value of rib height to channel hydraulic diameter ratio (e/D _h ) of 0.125. The importance of current work is to appraise the potential impact of rib geometry especially the p/e ratio on the heat transfer enhancement corresponds to square solid and continuous converging slit rib configurations. It is expected, that the experimental data generated from this study will broaden the understanding of heat transfer from fundamental perspective and will serve as a benchmark dataset for validation of computational models.

Mixed flow compressors are modified version of the centrifugal flow compressors and combine the advantages of axial and centrifugal flow compressors. The present work utilises a design methodology for the impeller of the mixed flow compressor such that it can work with an efficiency and mass flow rate close to axial flow compressor along with the pressure ratio per stage, resistance to foreign particles and ruggedness comparable to a centrifugal compressor. The focus is in understanding the various design philosophies and pick out one which best suits in accordance with available inputs and parameters. The design of the model is carried out in Ansys Bladegen. This is then meshed in Ansys Turbogrid and analysed in Ansys CFX. An analysis of flow in the impeller passage and the resulting parameters obtained are presented.

Jet from convergent nozzle under correctly expanded condition was controlled by two tabs kept opposite to each other with straight perforation and slanted perforation at different angles of 10°, 20° and 30°. This jet was compared with uncontrolled jet and jet with solid tab. It was found that jet with tab of slanted perforation 30° was having a lesser potential core as compared to jet with solid Tab. Further it was found that the effectiveness of the tab with slanted perforation increased with increasing slanted perforation angle. The streamwise vortices introduced by the slanted perforation in tabs were inclined towards the centreline of the jet and thereby causing the disturbance in potential core region of the primary jet and resulting in faster decay of the jet.

Turbocharging technique is widely employed in internal combustion engines to improve the performance and to reduce the exhaust emissions. Flow analysis through the turbocharger has been a guiding method to optimize the turbocharger design. Usually, the turbocharger turbine is analyzed at steady states. But in practical scenario the turbine operates with unsteady flow due to the reciprocating motion of exhaust port and creates unsteady environment in the turbine. In order to increase turbine efficiencies and effective engine turbocharger matching, proper understanding of unsteady flow physics within the turbine is essential. Currently the turbine and compressors maps are obtained by using 1D code which includes extrapolation techniques. These methods neglect heat transfer and windage effects, hence resulting in lower aerodynamic efficiencies. Three dimensional analysis could lead to a better estimation of the flow field, helping the designer to build a high efficiency turbocharger. The present article concentrates on investigating unsteady flow field in the turbine part of a turbocharger. The necessary unsteady conditions at turbine inlet were obtained using commercially available one dimensional engine simulation software AVL Boost. A turbocharged twin cylinder CRDI diesel engine test rig was modelled within the workspace. The exhaust mass flow rate, pressure and temperature were recorded as a function of crank angle. These results were used as the boundary condition for the 3D analysis of the turbine. ANSYS CFX tools were used to solve the unsteady case. The turbine geometry was generated using ANSYS bladegen. The model selected for analysis is k-ε turbulence Model. The pulsating performance, effect of secondary flows and entropy generation are discussed in the paper.

Film cooling is a proven cooling technique for gas turbine blades. The temperature distribution and flow phenomena vary with the suction and pressure sides. A computational investigation is carried out to understand the film cooling effectiveness and flow phenomenon on pressure side of a gas turbine aerofoil. A specific turbine blade profile is considered with combination of cylindrical and shaped holes in staggered fashion, oriented at different angles. Computations are carried out using the k-ϵ Realizable model available in the commercial code FLUENT 6.3. Meshing of the present model is done by using GAMBIT. The parameter variation considered for the present study is the blowing ratio (0.5–1.25) with an interval of 0.25 and three different density ratios (DR) 1.25, 1.5 and 2. The film cooling performance is discussed with effectiveness distribution on the interface wall. It is inferred that the film cooling performance enhances with increasing density ratio values. Also the optimum value of blowing ratio lies close to 0.75 for higher density ratio values of 2.

Horseshoe vortex is formed at the junction of an object immersed in fluid-flow and endwall as a result of three-dimensional boundary layer separation. When a boundary layer flow (either laminar or turbulent) encounters any obstacle projecting from the surface, some distance upstream of the obstacle the boundary layer separates as a result of the adverse pressure gradient, and rolls up to form three-dimensional complex vortices. Generally horseshoe vortex is observed near the endwall region and also forms near the tip endwall clearances. The passage flow is characterized by boundary layer effects, secondary flows generated by the pressure gradients, leading edge horseshoe vortex formation. The vortices form the characteristics of horseshoe shaped vortex, with legs of the vortices extending to downstream, on both sides of the blade. The numerical study was carried out for two turbine blades, considering the effect with and without endwall tip clearances from 0 to 5 % of span of the airfoil. The flow without tip clearance (c = 0 mm), will have maximum influence of the horseshoe vortex structure formation, because of strong pressure gradient observed near to the region to the blade leading edge. This affects the secondary flows in the endwall region, which implies more losses. And for the flow with higher clearances (c = 5 mm), it is observed that the horseshoe vortex formation in the leading edge of the blade is very weak, because of reduced adverse pressure gradient. The numerical simulation has been carried out for two turbine blades to study HSV structure and the interference effects on the blade flow characteristics. Additionally, the passage flow between the two turbine blades with and without endwall clearance effect is studied. Results of the numerical simulation of horseshoe vortex formation and effect of endwall clearances on the structures are presented. The velocity and static pressure are plotted and studied.

Engine exhaust stubs should be insulated to minimize heating of the nacelle. Nacelle material being aluminium the temperature rise due to hot exhaust gases should not deteriorate the characteristics of the aluminium material. To meet this requirement a heat shield should be installed on the portion of the engine exhaust duct internal to the nacelle. This paper describes aero-thermal relations used in selecting the insulation to protect exhaust ducts, assuming only the air flow due to natural convection and the emissivity of the duct material and the constraint is that the target cold surface temperature should be less than 200 °C. Having chosen the insulation, tests were conducted on the aircraft and the results show that the objective is met with the calculated target cold surface temperature limit.

This paper aims to provide a possible link of noise and vibration readings to the condition of pump operation. For this purpose, the dimensions of a radial flow pump impeller were determined using a flow rate of 0.031 m3/s, total head of 25 m and speed of 1500 rpm as the design data. Performance tests were conducted for this test pump with/without cavitation for different speeds. Noise and vibration signals were obtained and the individual critical frequency/critical frequency band were identified. From the results, it was concluded that the noise and vibration signature from the pump have a relationship with the flow inside the pump.

Latest technological tools of numerical simulation and experimental studies have been applied for the development of one of the world’s largest centrifugal pumps for a lift irrigation scheme. CFD Analysis has been used elaborately to iteratively analyze and optimize the design of various components of the pump. Results of numerical simulation have been validated by extensive experimental model studies. This paper describes the various technological aspects engrossing the design and development of these pumps. Salient design aspects of these pumps and the effects of design parameters on efficiency, safety, reliability and robustness have also been discussed. This paper also presents BHEL’s capabilities in delivering optimized solutions to real-time design problems and commitment towards endeavors of national interest.

This paper deals with a study of the effect of some turbine blade tip shapes on the secondary flows and the associated aerodynamics. A conventional plain tip shape and a novel squealer tip shape are compared aerodynamically using numerical analysis. The simulations are done using a finite volume-based, general purpose CFD solver, ANSYS FLUENT. The investigation was carried out on a turbine blade cascade consisting of three blades, test blade being the central blade which was modelled. The cascade analysis was done to capture the secondary flows and associated losses. Two cases of tip clearance viz., 0 and 1.5 % of the blade span were considered in this study contributing to the effect of blade tip geometry. The vorticity magnitude at a selected downstream vertical plane was estimated to aerodynamically compare the tip shapes employed in this study. Due to tip clearance, local secondary flows are found to be generated at the blade tip region. Results obtained in this study further indicate that squealer blade tip reduces the secondary flow losses when compared to the conventional plain turbine blade tips. Reduction in secondary flow losses is expected to subdue the effect of heat loads on blade tips. This is perhaps the most prominent practical implication of this key result. The magnitude of vorticity at the blade tip region for squealer tip with 1.5 % tip clearance is 21.25 % less than that for plain tip at the blade tip region for the same tip clearance. This is possibly because of separation of flow and recirculation at the squealer rim which induces weak leakage flows.

In mini/micro hydro schemes, centrifugal pump can be used as hydraulic turbine in view of its similarity with Francis turbine and various advantages associated with pumps. At present, standards are not available for design of draft tube for pump as turbine (PAT). Hence, current trend is to use the standards available for hydraulic turbines. Improper selection of draft tube may lead to huge vibrations in system; which may affect life as well as overall performance of the system. Researchers have used either straight or diverging draft tube for PAT. It is required to access necessity of diverging draft tube for PAT in view of performance, life and cost involved with it. In this paper, performance of PAT studied with straight and diverging draft tubes in terms of operating characteristics and vibration analysis are presented. Analysis concluded that, PAT works more efficiently with diverging draft tube and subjected to lesser vibrations.

Regenerative pumps are low specific speed pumps which are used for high head at smaller flow rates. These pumps are self-priming and can operate at low NPSH. These pumps can deliver head much higher than any other centrifugal pump with same tip speed. In spite of all these they are low on efficiency point of view. This paper describes the CFD simulation of a regenerative pump and its comparison with the experiment results. Based on these results, a new pump is designed. The effect of vane thickness variation and side channel width variation on its performance is studied through numerical techniques.

The buckling load is an important parameter necessary for designing a multistage hydraulic cylinder (telescopic cylinder). There are very few methods available to analyze the buckling load of a hydraulic cylinder. In the present work for a typical multistage cylinder, critical buckling load has been analyzed using strain energy method, weighted moment of inertia method and finite element method. The critical buckling load obtained by the energy method and weighted MOI methods are compared using ANSYS finite element analysis. The results and conclusion are presented.

The effect of variation of diffuser radius ratio on the performance of a centrifugal compressor stage with vaneless diffuser (VLD), low solidity vaned diffuser (LSVD), and twisted vaned diffuser (TVD) was studied using Computational Fluid Dynamics (CFD). ANSYS CFX software was used in the present study. The diffuser vane was generated by modifying the trailing edge of a cambered aerofoil profile (NACA 2410). The stagger angle was varied from hub to shroud forming a twisted vane diffuser keeping the same leading edge. The present analysis was carried out at a tip Mach number of 0.35. The performance was assessed in terms of stage power coefficient, stage efficiency, total pressure loss coefficient and static pressure recovery coefficient for five different flow coefficients in the diffuser. From the present study, the optimum radius ratio is 1.10 for TVD with the chosen impeller diffuser configuration.

An axial gas turbine stage with disc cavity was numerically investigated to assess the effect of purge flow on cooling of turbine disc and rotor blades, and on turbine overall performance. Steady state flow analysis was carried out using ANSYS FLUENT software without purge flow, and with three purge flow rates of 7, 6.5 and 5.75 % of the primary turbine design mass flow rate. The purge flow from disc cavity, driven by the pressure differential, combines with and affects the main annulus flow. At any purge flow rate, the turbine efficiency continuously drops with increasing pressure ratio owing to reduced cooling effect. The purge flow causes compression of the primary gas flow, resulting in higher static pressure and temperature above mid-span level of the rotor blade compared to the case without purge flow. However, the rotor blade temperature is reduced in the hub region where the stresses are large. The cooling is found to be more pronounced on the suction surface of the rotor blade than on the pressure surface. Flow through the disc cavity shows complex behaviour with dominant recirculation zones. It is concluded that the turbine efficiency as well as the blade surface temperature distribution is affected by purge flow and that the overall turbine performance is sensitive to both modeling assumptions and cooling flow rate.

Counter rotating turbine is an axial turbine with nozzle followed by a rotor and another rotor that rotates in the opposite direction of the first one. Studies show that speed ratio and stagger angle are the two important parameters that affect the performance of a turbomachine. Present work involves computationally studying the performance and flow field of CRT for different speed ratios and stagger angles. Turbine components nozzle, rotor 1 and rotor 2 are modeled for the cases of CRT with and without staggering. Total pressure and entropy distributions across the blade rows are used to describe the flow through CRT. Enthalpy losses and TKE are estimated at the exit of the blade rows and performance curves are plotted for all the configurations. Results show that the flow composition in rotors varied with speed ratio and improved at the inlet of the second rotor in staggering cases. Due to this the performance of rotor 2 and CRT improved with speed ratio and staggering. Results confirm the beneficial aspect of varying speeds and staggering of second rotor in CRT.

Numerical solution of governing equations of two-phase immiscible flow in porous media is presented. The mathematical equations are built by combining the conservation of mass with Darcys law which describes fluid flow through porous media. The resulting partial differential equations were solved using Implicit Pressure and Explicit Saturation method (IMPES). We have implemented the IMPES method in open source CFD toolbox OpenFOAM, which uses finite volume method to solve PDEs. The underlying advantage of using general purpose CFD solver for reservoir simulation is the possible extension of simulation technique to enhanced oil recovery methods involving simultaneous fluid flow, heat transfer, mass transfer and chemical reactions. Simulations were carried out for water displacing oil in homogeneous as well as heterogeneous reservoirs. The simulation method was validated by comparing the results with analytical solution and numerical solution of Matlab Reservoir Simulation Toolbox (MRST). The displacement efficiency and water breakthrough of various flooding patterns were evaluated.

An experimental investigation is performed to study the bursting of the Taylor bubble at free surface and film collapse around the bubble. The study is conducted for only circular tube in vertical position with different liquids (water, mustard oil, glycerin, and silicon oil) as bulk. Experimentally collapse of Taylor bubble is tracked at the free surface with different tube diameters (19 and 28 mm) by proper arrangement of high speed camera (3000 frames/s) and light. Profile contour of bubble at different stages of bursting process is traced which reveals bubble top film and wall thickness variation with time. Behavior of Taylor bubble collapse in different liquids is explained thoroughly by using visualization and photographic recording technique.

Drop impact on surfaces is a key area of interest since the pioneering works by Worthington in the 1800s and plays an essential role in modeling the spray drop interaction with solid surfaces. The present study is an experimental investigation of the impingement of Jet A-1 drop on smooth stainless steel surface with Weber number, We ranging from 25 to 570. High speed digital imaging as well as video microscopy is employed to study the various characteristics of the interaction process. Primary measurements extracted from the high speed frames of drop impact process included the trends of drop size and impact velocity with impact height, and the temporal variation of spread factor of drop on the stainless steel surface. Secondary measurements extracted from these, to elucidate the various features of drop impact dynamics, included the power dependence of spread factor on time and the average rate of spreading during the spreading phase, maximum spread, time taken for attaining maximum spread, and the final spread. Trends highlighting the variation of these secondary measurements with the impact velocity were also obtained. Comparisons of the observed trends of secondary measurements with theoretical and semi-empirical models reported in literature were performed to study the suitability of application of these models to the impact dynamics of Jet A-1 drop on the target surface.

The relative motion between swarms of bubbles and a contaminated power-law fluid is numerically investigated using a computational fluid dynamic based approach. The effects of bubble holdup and the degree of contamination are incorporated in the solver by means of a cell model and spherical stagnant cap model, respectively. The continuity and momentum equations are solved using a finite difference method based semi-implicit simplified marker and cell method (SMAC) on a staggered grid arrangement in spherical coordinates. The final steady velocity and pressure fields are used to delineate effects of Reynolds number (Re: 1–200), bubble holdup (Φ: 0.1–0.5), power law index (n: 0.6–0.8), and stagnant cap angle (α: 0°–180°) on streamlines, vorticity contours, surface vorticity and drag coefficients of contaminated bubbles.

Present study is a numerical effort towards capturing the evolving and topologically complex interfacial behavior of a Taylor Bubble while it is passing through an orifice like constriction in a vertical tube. These simulations are performed using the adaptive, incompressible quad tree based 2D axis-symmetric Gerris solver (Popinet, J Comput Phys 228(16):5838–5866, 2009 [1]) which is based on classical geometrical VOF scheme that proceeds in two steps i.e. reconstruction of the interface and advection of the same followed by computation of mass flux. The crucial involvement of interfacial surface tension in controlling the hydrodynamics of the phenomena is taken care of by making necessary modifications to the momentum equation based on the continuum surface force (CSF) concept coined by Brackbill et al. (J Comput Phys 100(2) 335–354, 1992 [2]). After volume fraction calculation, the interface reconstruction is achieved using a second order accurate height-function (HF) method which ensures an improved extent of volume flux conservation for the VOF scheme. Initially the axis-symmetric code has been developed for the uprise of both spherical as well as Taylor Bubble in a straight vertical channel and then the obtained results have been validated against the available velocity correlations for respective cases. After the validation we moved on to incorporate the effect of constriction in the passage on interface dynamics. Simulations have been carried out for a wide variation of constriction ratio as well as fluid properties to capture the dependence on each critical parameter properly. Observed trends came to be satisfactory as per the expectations.

For the past two decades LBM has been interest of research for handling multiphase and multicomponent fluid flows. The pseudo-potential model is a widely used multiphase Lattice Boltzmann model based on the Equation of State (EOS) proposed by Shan and Chen. In the multiphase LB model, an interaction force between the molecules is being incorporated using a forcing scheme that automatically cause phase separation without tracking the interface. In this paper three different forcing schemes: the Discrete Force Method, Velocity Shift Method and Exact Difference Method are evaluated to study their effect on relaxation parameter. The spurious currents are estimated for different values of relaxation parameters. SCEOS is found to be stable with all forcing schemes at lower liquid to gas density ratios when viscosity ratio is set to unity. Numerical simulations were performed on D2Q9 lattice structure. The density and kinematic viscosity ratios between the liquid and gas phases were maintained at 50 and 5 respectively.

The concurrent flow of two different liquid or gaseous phases is termed as two phase flow. The study of two phase flow is important due to its wide applications in industries. Its applications include cooling, refrigeration, atomization of fuels, chemical processing and cryogenics. Study of two phase flow parameters such as velocity and length of two phase slug flow pattern is significant in analyzing the heat transfer characteristics in the case of refrigeration and chemical process industries. In the present study, a pair of infrared emitter and receivers is used to determine the velocity and the length of a slug type two phase flow. By knowing the distance between the IR pairs and by calculating the time taken using a DAQ, velocity and length can be determined. Image processing and high speed videography technique is used to validate the obtained results.

This paper describes issues related to implementation of Modified-Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM) which bestows the effect of CICSAM and High Resolution Interface Capturing Schemes (HRIC). Among the two, CICSAM has a very good shape preserving characteristics while HRIC is less dependent on cell Courant number. The modified scheme is tested for three-dimensional deformations. The developed algorithm is coupled with a Navier-Stokes flow solver to simulate flows pertaining to high surface-tension. High surface tension problems are difficult to be captured when the surface-tension is treated as an ordinary source term as it tends to generate unphysical velocities. In the present work influence of surface tension is implemented using Balance Force Algorithm along with Continuum Surface Force (CSF) model. The developed algorithm is successfully tested for three-dimensional static bubble test with surface tension co-efficient of seventy three and rise of air bubble in water.

The study on injection of supercritical fluid into subcritical and supercritical environment involves dependence of fluid dynamic processes on thermodynamic transition. Beyond the thermodynamic critical point, the fluid exists in single phase known as supercritical fluid with its properties that are entirely different from liquid and gases. The surface tension and latent heat of evaporation is absent at the critical point. In this study, the transition of supercritical elliptical jet injected into subcritical environment as well as supercritical environment is investigated experimentally. Beyond the critical temperature, the axis switching is not observed. The investigation also shows that pressure plays a greater role in determining the thermodynamic transition in the elliptical jet. At larger supercritical pressure, the supercritical jet undergoes formation of droplets in the subcritical environment. However, for supercritical jet injection into supercritical environment, the gas-gas like mixing behavior is observed.

High fidelity computational modeling of positive displacement pumps based on Reynolds Averaged Navier-Stokes (RANS) equations on unstructured meshes using the finite volume method with the aim of extracting performance characteristics of different types of positive displacement pump is addressed in this study. The interface between the liquid and air is captured with Volume of Fluid (VOF) methods. Turbulence is modelled using a two equation k-ɛ RANS model. Overset mesh technique is used to facilitate motion of various pump components in the computational study which also accounts for leakage between components.

Interactions between liquids and solids are ubiquitous in our physical environment. A sessile droplet on a homogenous and smooth surface is known to minimize its liquid-vapor interface area and assume a spherical cap shape. However, practical engineering applications involve fluid flow over rough and heterogeneous surfaces and the curvature varies along the liquid-vapor interface. Despite significant efforts over the past few decades, a comprehensive model, that, while capturing the complex dynamics at the three-phase contact line, is also able to predict the apparent contact angle values typically observed in experiments, is missing. In this work, we use vector valued parameterized cubic spline-based representation to model the droplet shapes on rough and heterogeneous surfaces. Thermodynamics driven minimization of the free energy via the minimization of the liquid-vapor interface area in three dimensions is reduced to the minimization of the perimeter of the liquid-vapor interface in this case. We show that the minimization of the perimeter is mathematically equivalent to the minimization of the spread in the curvature along the liquid-vapor interface. The shape of the resulting interface near the three-phase contact line is shown to resemble the shapes typically observed during high resolution microscopic contact angle experiments. Moreover, the contact angles estimated by approximating the obtained droplet profiles using circular arcs are found to match the average contact angle values in experiments. We believe that this simple and computationally inexpensive approach can be used to understand nature’s design and extend it to enable fine fluidic manipulation capability in biological, manufacturing, microfluidic, and thermal management applications.

In this paper, the dynamics of a gas bubble rising in a quiescent fluid column is presented. Numerical simulation has been performed and the interface between the two phases is tracked with Volume of Fluid (VOF) method with Continuous Surface Force (CSF) model. Newtonian flows are solved using finite volume scheme based on the Pressure Implicit with Splitting of Operators (PISO) algorithm. The interFoam solver of OpenFOAM, an open source computational dynamics software, is used to simulate the rising bubble phenomenon. The numerical method uses an additional surface compression term in the phase fraction equation which improves the interface capturing algorithm by reducing the smearing of the interface. The results of a benchmark paper are validated and presented in this work.

Development of bedforms is studied in curvilinear sand bed threshold channel with uniform sand (d₅₀ = 0.418 mm). In this study, two types of experiments have been carried out no seepage (NS) and with downward seepage or suction (WS). Present experimental study investigates the development of bedforms and turbulent characteristics in a threshold channel after applying the suction. Value of bed shear stress measured at temporal basis with suction initially increases with time. Once the channel attains near stability with application of seepage, Reynolds stresses decrease. Measurements have shown that turbulent intensities initially increased due to seepage and reduced when channel was subjected to downward seepage further, which probably shows that migration rate of bedforms is reduced. Features of bedforms geometry start with small in size in which they propagate from upstream to downstream.

Rotary Desiccant wheel in the desiccant air conditioning system is used for the dehumidification of process air by adsorption of water vapour by the desiccant (porous media) layer. And while the hot air which is heated up by the heater (or waste heat recovered from other equipments) flows through regeneration side, water is desorbed out from the desiccant and gets regenerated. In a desiccant wheel, the process air enters the wheel at one end with high moisture content and the moisture is continuously transferred from air to desiccant. Since, the equilibrium adsorption capacity of desiccant material is directly proportional to the relative humidity of air in contact, the rate of moisture transfer decreases along the width of the wheel. This is considered to be a bottleneck for the efficiency of a rotary desiccant wheel where improvements can be done. The innovative design of rotary desiccant wheel presented in this paper enhances the moisture removal capacity by using multiple desiccant materials over the width of the wheel and increases the moisture removal capacity and efficiency of the wheel without increasing the overall dimensions of rotary desiccant wheel. The numerical results of this multiple desiccant wheels (Hybrid) are compared with conventional wheel made up of either molecular sieves or Silica gel. The results show that the performance of the wheel can be enhanced by 10–25 % by using this innovative design. The governing equations of heat and moisture transfer are discretized using the finite volume method and the simulations are carried out using a code developed in FORTRAN 95.

The present work discusses the role of orifice recess on the drop size characteristics of sprays discharging from gas centered swirl coaxial (GCSC) injectors used in liquid propellant rocket engines. Four GCSC injectors (one coplanar and three recessed) are considered. The experiments are conducted in a spray test facility with water and air as experimental fluids. The measurements of spray drop size are obtained using laser diffraction based Spraytec. The spray flow is characterized in terms of the gas-to-liquid momentum flux ratio, J. For a given GCSC injector, the measured SMD for sprays discharging from the injector decreases with increasing J. The sprays discharging from the coplanar CGCS injector exhibit typical uni-modal drop size distribution. However, the sprays discharging from the recessed GCSC injectors exhibit a bi-modal drop size distribution and the existence of bi-modality gets stronger with increasing J. Detailed analysis is made to shed lights on the mechanisms of spray formation in recessed GCSC injectors.

The study of dispersed laminar gas-particle flow in a horizontal channel is carried out using finite volume method on unstructured grid. In this context, Eulerian-Eulerian two-fluid model is employed to analyze the flow behaviour of both the phases inside the flow domain. The interaction between the gas phase and the particle phase is taken care by introducing the drag force term in their governing equations. The behavior of the particle phase when released at a low velocity into a uniform fluid flow is analyzed for particles having different sets of diameters. It has been found that for the particles of same material density, particle diameter plays an important role in the amount of drag force experienced by the particle phase dispersed in a continuous fluid medium.

In the present work for numerically investigating the interfacial flows, an algebraic Volume of Fluid technique has been implemented over hybrid unstructured meshes. Following the work of Dalal et al. (Numer Heat Transf Part B 54(2):238–259, 2008 [2]), the governing equations are discretised by cell centered finite volume method wherein pressure-velocity coupling has been achieved by momentum interpolation due to Rhie and Chow (AIAA J 21:1525–1532, 1983 [12]). The binary fluid problem is represented by a single fluid formulation with a fluid property jump at the interface. Two schemes namely NVD based GAMMA scheme (Jasak, Int J Numer Meth Fluids 31:431–449, 1999 [7]) and Convergent and Universally Bounded Interpolation Scheme for the Treatment of Advection (CUBISTA) (Alves et al., Numer Heat Transf 49:19–42, 2006 [1]) has been incorporated into an in-house fully coupled Navier-Stokes solver. These schemes are validated with the published results of collapse of water column also known as dam break problem by Martin and Moyce (Math Phys Sci 244:312–324, 1952 [9]) and Rayleigh-Taylor instability (Tryggvason, J Comput Phys 75:253–282, 1988 [13]). The results are found to be in good agreement.

The capillarity induced resonance has been one of the promising method as far as the mobilization of trapped blob is concerned. In this context, lattice Boltzmann Shan and Chen model is employed to analyze the movement of a 3-D immiscible blob influenced by oscillatory acoustic excitation in a tube. The influence of the physicochemical parameters which includes wettability, width of tube, viscosity, magnitude of the force and frequency on blob dynamics are discussed. The effect of frequency on the blob shows peak displacement of the blob at resonance frequency. The resonance behaviour of blob with various wettabilities and capillary numbers is analyzed to understand capillarity-wettability interaction. Mobilization study of the blob reveals that wettability plays a crucial role in the blob mobilization at low capillary number.

In the present study, an experimental investigation has been carried out to analyze the effect of jet inclination on the heat transfer characteristics of a vertical hot surface during circular free impinging liquid jet. A rectangular stainless steel foil (AISI-304, 0.15 mm thick), used as the target surface, was electrically heated to an initial temperature of 400 °C. A single-phase circular water jet of diameter 1.38 mm is allowed to impinge on the hot surface. Infrared thermal camera (A655sc, FLIR System) is used to record the thermal images of the target surface during liquid jet impingement. The distribution of heat flux on the target surface is evaluated from the thermal images, recorded during transient cooling experiments. Tests were performed for an initial surface temperature of 400 °C, Reynolds number $$\left( {8893 \le Re \le 12847} \right)$$8893≤Re≤12847, and nozzle to plate distance $$\left( {2.5 \le l/d \le 4.5} \right)$$2.5≤l/d≤4.5 and jet inclination (0 ≤ α ≤ 45°). The heat flux is found to be maximum at stagnation point for the jet inclination of 30°. It is observed that the jet to plate spacing has minimal effect of stagnation point maximum heat flux.

The present work investigates the spreading, receding and bouncing dynamics of a droplet falling on a superhydrophobic substrate. CMFD (computational multi-fluid dynamics) simulations are done using a DGLSM (dual grid level set method) based in-house code in an axisymmetric cylindrical coordinates. The available dynamic contact angle model from the literature is implemented in the code—to capture dynamic wetting of the droplet on the substrate. The deforming liquid-gas interface—during the droplet impact—is tracked using zero level set function. The droplet impact is modelled such that liquid vapor diffusion in the atmosphere, viscosity and surface tension variation with temperature are considered negligible. The droplet, substrate and surrounding air are at atmospheric conditions. Advancing and the receding contact angle of the droplet with the substrate (i.e. the wettability of substrate) are found to play a vital role in the modeling of impact dynamics of droplet. Numerically obtained temporal evolutions of the droplets are compared with published experimental results; for bouncing as well as non-bouncing droplets. Other than the instantaneous interface shape, the comparison is also done for temporal variation of droplet height and wetting diameter. The comparison is good—validating our DGLSM for the impact-dynamics.

In order to improve the mixing efficiency and therefore the quality of steel, “bottom blowing” technique has been widely used in Basic Oxygen Furnace (BOF) steel making process. The main objective of the “bottom blowing” is to provide efficient mixing and homogeneity in the metal bath that increases overall process kinetics as well as reduces levels of impurities (i.e., C, Mn, P, S, Si, etc.). In the present study, three-dimensional transient Euler-Lagrange simulations were performed for mono-dispersed cold gas-liquid flow in 6:1 scaled-down BOF steel converter to predict the dynamics of gas-liquid flow with only “bottom blowing”. Cold flow experiments were also performed in the BOF vessel to verify predicted time-averaged gas volume fraction at different gas flow rates. “In-house” developed voidage probes were used for measurements of local gas volume fractions at different axial locations along the height of the BOF vessel. Effect of various numerical models and schemes used in the simulation e.g. effects of grid size, number of particles per parcel, particle time step etc. on the dynamics and time-averaged flow properties were investigated. Typical results showed that predicted time-averaged gas volume fraction profiles at different gas flow rates were in a good agreement with the measurements.

The unsaturated soil zones beneath the earth surface are vulnerable to several types of harmful and toxic contaminant movements due to various natural and anthropogenic interventions. The convective-dispersive equation, which is traditionally used to describe the contaminant movement in porous media, has drawbacks of prediction in contaminant concentrations that are influenced by physical non-equilibrium that may exist due to presence of mobile and immobile liquids in the void spaces. We attempt in this paper to analyze the influence of physical non-equilibrium in pore water on acid mine drainage (AMD) through unsaturated soils. The United States-Environmental Protection Agency (US-EPA) developed finite-element software FEMWATER, which solves the liquid flow and contaminant specie transport using finite-element methods, is modified to incorporate features of physical non-equilibrium in contaminant transport due to AMD.

Long gas bubbles in circular tubes, called Taylor bubbles, occur frequently in industrial applications. If the tube contains two immiscible liquids, one on top of the other, a rising Taylor bubble after passing though the interface entrains some heavier liquid that was below the interface into the liquid that is above the interface. This article reports different shapes and sizes of the entrained mass as it rises sticking to the tail of rising Taylor bubbles of different volumes.

The focus of the present work is to develop a robust algorithm for simulation of stationary/moving rigid solid object(s) in free surface flows. The algorithm is based on incompressible finite volume hybrid staggered/non-staggered framework and captures the fluid–fluid interface using the Volume-of-Fluid (VOF) method by solving advection equation for volume fraction with velocity obtained from the Navier–Stokes equations. A novel interface capturing scheme CUIBS (Cubic upwind interpolation blended scheme) is employed to preserve the sharpness of the interface. Presence of the object(s) are accounted through solid fraction, which is advected with the object velocity, either prescribed or calculated from the equations of solid dynamics. A diffuse interface immersed boundary method is employed to solve the normal momentum equation. The present formulation gives liberty to execute normal momentum and pressure correction equation every where in the domain, considering imaginary fluid inside the solid object with dynamic viscosity of heaviest fluid and density of lightest fluid. The algorithm is applied to the benchmark problems involving the flow past a stationary cylinder and water entry of a cylinder. The numerical experiment on the sedimentation of two particles is investigated to analyse the efficacy of present algorithm.

We consider the motion of the drop sedimenting down an inclined glass plate in viscous fluid. The density difference between the two fluids causes the motion of the drop along the glass plate. The drop motion for Reynolds number, Re << 1 and Bond number, B << 1 for inclination angle, 0.174 < α < 0.523 was studied. In that regime, Stokes drag over the drop balances the driving force. The proposed scaling law was compared with Hodges theoretical relation and with the experiments. The outer flow field visualization of the drop was done using particle imaging velocimetry technique. A small recirculation zone was observed just above the drop from the PIV image.

The present work focuses on the characteristics of cavity flow with fore wall modifications in a blow down type non-reacting supersonic flow facility. The facility consists of a supersonic nozzle which provides a flow Mach number of 1.44, a stagnation pressure of 0.38 MPa and a total temperature of 300 K. A supersonic combustor of circular cross section, 26 mm in diameter and 130 mm in length, was integrated with the nozzle. Axisymmetric aft ramp cavities of varying depth and ramp angles were placed inside the combustor at a distance of 30 mm from the inlet. A constant fillet dimension of 3 mm at the fore wall of the cavity was used for the investigation. Fore wall fillet cavities provide more fluid entrainment than that absence of fore wall modification with marginal increase in stagnation pressure loss.

The purpose of this study is to analyse the effect of damping length on a two-stage two-spool electrohydraulic servovalve controlled by a pressure control pilot. This nonconventional servovalve comprises of two spools instead of one which serves to meter flow into and out of the valve separately. There is no feedback wire, the pressure difference between two chamber acts as a feedback element. This non conventional servovalve is easy to manufacture, gives greater safety and reduces the valve cost substantially. A simplified linear model is developed to capture the effect of damping length on the dynamic performance of the system. The model has been coded in Matlab/simulink taking into account the effect of axial flow force and fluid compressibility.

An adaptive fuzzy sliding mode controller with fixed bias compensator is designed in this paper to address the issue of position control of an electrohydraulic actuation system. The adaptive fuzzy sliding mode controller approximately compensates for the system nonlinearities and minimizes the approximation errors. In order to attenuate the effects of discontinuous nonlinearities, the fixed bias compensator is introduced. The adaptation scheme is based on the Lyapunov function of the sliding function variable drawn up with Hurwitz coefficients, thereby ensuring the closed loop stability and convergence. Real time experiments conducted on an existing electrohydraulic laboratory set up comprising of a proportional valve and a single-rod cylinder evince that the proposed control method is robust for diverse range of demands.

The focus of present study is to have a comprehensible understanding of flow physics involved in separation in rocket nozzle. Numerical analysis of flow separation in rocket nozzles is challenging and involved task because of the complex turbulent flow behaviour that develops different shock-patterns. The study will have to consider shock-boundary layer interaction with shear layers and formation of vortices that includes the generation of flow features like the Mach disk, separation shock, Mach stem, vortex core, contact surface, slip stream and shock front. When the back pressure is high enough, the boundary layer separates and moves freely away from the nozzle wall. A recirculation zone of ambient air is created at the nozzle exit which will not allow the flow reattachment. This is a basic separation pattern, commonly known as Free Shock Separation (FSS) that can be observed in all kinds of nozzles; especially, conical, contoured or Truncated Ideal Contoured (TIC) nozzles. The flow separation pattern is considerably different in strongly overexpanded nozzles with an internal shock, like Thrust Optimized Contoured nozzles (TOC) or Thrust Optimized Parabolic bell nozzles (TOP). The flow is getting reattached to the nozzle wall creating a restricted circulation region forming a closed separation bubble and is named as Restricted Shock Separation (RSS). The paper presents numerical simulations carried out with different nozzle geometries and chamber-to-ambient pressure ratios with comprehensive assessment of the flow features and flow separation structures. Separation of supersonic flow in convergent–divergent nozzles is investigated by solving the Reynolds-averaged Navier–Stokes equations with a two-equation k-ω turbulence model.

The present work is an experimental study of flow past a finite circular cylinder, carried out in a low speed wind tunnel. Force measurement was carried-out to study the effect of free end on static and dynamic behaviour of finite cylinders of different aspect ratios from 6 to 14. PIV measurement was also carried-out to observe the nature of flow near the free end of the finite cylinder. A strong downwash and back-flow was observed in the central wake plane near the free end. Based on the observations, a thin circular disc has been implemented as a flow control device, which has been found to be effective in suppression of the cross-wind force.

Circular cylinders experiencing different levels of free stream turbulence for Reynolds number (Re) varying from 500 to 32,000 have been studied in the present study using a multi-channel hotwire anemometry system and the smoke flow visualizations. A wire mesh (gird) is placed at the entrance of the test section for varying the free stream turbulence (FST) inside the test section. The circular cylinders are placed at various downstream locations where the turbulence intensity is known for studying the effect of FST. The turbulence statistics, vortex shedding behind the circular cylinder, variation of wake profile and the flow visualizations are used for characterizing the effect of FST.

Flow control by the confined effect of the counter-rotating side/control cylinders (deceleration of the gap-flow), on the free stream flow across a stationary/main cylinder is studied numerically. The study is done for various rotational speeds $$ \alpha ( \equiv \omega d/2u_{\infty } ) = 2 - 7 $$α(≡ωd/2u∞)=2-7 and cylinder spacing $$ (s/d) = 2 - 5 $$(s/d)=2-5 at Reynolds number $$ (\text{Re} = u_{\infty } d/\nu ) $$(Re=u∞d/ν) of 100. Various types steady and unsteady flow regimes are reported for the main as well as control cylinder, with increasing rotational velocity of the control cylinder at various cylinder spacing. The results are presented with the help of flow regime map. Unsteady and unsteady flow patterns are demonstrated with the help of streamlines, vorticity contours and wake. Substantial drag reduction is found for the main under the influence of rotating control cylinder; with thrust generation at larger rotational velocity of control cylinder. The flow transitions for the rotating control cylinder of same size is not available in the published literature.

A parametric study has been done for a fluid-elastic system consisting of a clamped annular circular plate backed by two cavities by varying the system parameters based on an analytical formulation. The quantification of the coupled frequencies mainly depends on coupling of the acoustic and structural modes. Key parameters like geometry, speed of sound and fluid density influence this coupling significantly. Analysis of this coupling is done by means of a parametric study. The coupling effect in general will be manifested as an added stiffness effect or an added mass effect.

Flow over a square prism with attached splitter plate is investigated at Reynolds number 485. Splitter plate attached on the base of a square prism acts as a control for wake modification. By varying the splitter plate length the wake structure can be manipulated according to the need. In present study, we investigated the effect of splitter plate length attached to a square prism using Particle image velocimetry (PIV) and flow visualization techniques. The results are compared for both configurations with and without splitter plate. The length of the splitter plate are varies over wide range (L/D = 0−5) to characterize the near wake structure. Splitter plate thickness kept nominal with respect to cylinder size (0.1D). Increase in length of splitter plate changes the shear layer roll up distance and hence vortex formation region. Drag coefficient is reduced up to 41 % with the splitter plate as compared to prism without splitter plate. The detailed flow structures are investigated from flow visualization, velocity contours and vorticity contours.

When two cylinders are in proximity with each other the vortex shedding of one cylinder are influenced by the other. The flow field becomes even more complex when one cylinder subjected to an oscillation. In present study flow around two inline square cylinders of aspect ratio 50 at different spacing ratio is investigated experimentally. Experiments are performed for two identical square cylinders of 6 mm diameter at Reynolds number 500 in a low speed wind tunnel using Particle image velocimetry (PIV) and hotwire anemometer (HWA). The upstream cylinder is given predetermined oscillation and the gap between the two cylinders varied over wide range. Present study focused on effect of forcing frequency and spacing between centers of two cylinders (s/D = 1.5–5.0). The upstream cylinder is oscillated in transverse direction at f/f₀ = 0 to 2 and the effect of this oscillation is observed behind the downstream stationary cylinder at different spacing of the cylinders by hotwire.

Manipulation of fluids in smaller scales has become an extensive field of research for miniaturization of devices in order to cope with the growing demand of modern human civilization. Among other techniques, electro-wetting is the well accepted due to its relatively higher precision and reliability. There are various parameters which could influence electro-wetting process; type of surfaces, whether hydrophobic or hydrophilic is one of them. Hydrophilic surfaces retains a lower contact angle, when get in touch with a liquid droplet; whereas, hydrophobic surface maintains a higher contact angle. In the present study influence of surface contact angles on droplet motion along inclines has been investigated in an analytical approach. A momentum equation which could comprise the effect of contact angle change is solved to study the influence of different contact angles. The contact angle has been varied from 30–120º. The variation of velocity has been analysed for a voltage range of 0–100 V. It has been observed that increase in droplet foot print causes enhancement in actuation force for climbing.

In the present experimental work a comparative study has been done to investigate the effects of single phase and flow boiling heat transfer performance of straight, uniform and expanding cross-section microchannels. Two configurations of microchannels have been fabricated on individual copper substrate (25.7 mm × 12.02 mm). In both types of geometry, 12 channels of rectangular cross-section have been fabricated having cross-section is uniform and expanding. Width at the inlet is 400 μm for both of channels and depth is 750 μm. Subcooled, deionized water with inlet temperature of 27 °C has been used. Heat transfer analysis revealed that performance of diverging channel is minimal higher for flow boiling case only, at high heat flux and low mass flow rate. For single phase convective heating its performance is not appreciable.

Drying of a colloidal droplet on solid surface leaves a ring like deposits. The deposition pattern depends on the fluid flow inside the droplet during drying process. The 3D flow field inside the droplet of pinned contact line is reported using micro-PIV technique. Fluid flow towards the contact line is observed to be responsible for the ring like deposition pattern. The magnitude of the velocity is observed to be more near the contact line.

In this paper, an analytical study has been carried out to investigate the effect of viscous dissipation on heat transfer characteristics in the slip regime for the fluid flowing between two infinite fixed parallel plates. The flow is assumed to be hydrodynamically and thermally fully developed with constant properties. In the present analysis, one wall is considered as adiabatic and the other one is kept at constant heat flux. Closed form expressions are accomplished for the Nusselt number as a function of Knudsen number and Brinkman number. The limiting condition of the present prediction for Kn = 0, Kn2 = 0, and Br = 0 is presented to verify the results.

Ferrofluid plug driven micro-pumps are useful for manipulating micro-volume of liquids by providing remote actuation using a localized magnetic field gradient. Inside a microchannel, the ferrofluid experiences combined actions of different relevant body forces. While the pressure, viscous and magnetic forces can be estimated using established techniques, surface tension force cannot be readily. The presence of a second fluid (the fluid being pumped) and magnetic field (the driving dipole) alters the ferrofluid-wall contact angle (CA) in both static and dynamic fashions, which has not been reported in the literature. Therefore, realistic prediction of ferrofluid-plug driven micropump requires comprehensive data on variation of CA between the ferrofluid and glass capillary wall under different kinematic conditions. Here we perform an experimental characterization of static and dynamic contact angles of oil-based ferrofluid (EFH3) droplets on glass surface immersed in pure or surfacted distilled water. The relation between CA and the contact line velocity for ferrofluids is particularly important as the observed CA values fell beyond the classical Hoffman-Tanner equation. In the presence of an external magnetic field, a sessile ferrofluid droplet is seen to acquire interesting shapes. Growth of a droplet due to pumping of fluid from below the surface leads to a pinning and de-pinning effect. Our results also show a decrease in contact angle hysteresis (CAH) at higher contact line velocities as the droplets slide down an inclined plane.

Practical applications involving lab-on-a-chip devices in microfluidics demand a variety of manipulation to be done on liquid drops on a solid surface including drop transport from one location to another. Wettability gradient surfaces, featuring a spatial variation of surface wetting along a particular direction on the surface, are commonly used to achieve this goal. In this study, we investigate the spreading process of liquid drops impacting, with velocity U _o in the range 0.3-1.5 m/s, on the junction of a dual-textured surface comprising a textured portion and a smooth portion of different wetting characteristics. Comparisons with the results for drop impact under same impact velocities on the homogeneous (far away from the junction) textured and smooth portions of dual-textured surface are also made to understand the effect of the dual-texture nature of target surface on drop spreading process. The drop spread factor, β increases with normalized time, τ as τ0.5 in the initial kinematic phase on all the surfaces whereas for the entire spreading process the power reaches 0.5 as impact velocity is increased. Even though the average spreading velocity, which shows a slight decrease with U _o , does not show any significant difference between the surfaces, the drops impacted on textured surfaces (homogeneous and dual-textured) show a slightly higher deceleration than on the corresponding smooth surfaces. The maximum drop spread and the time taken to attain it are seen to be lower on the textured surfaces; however no difference is seen between the homogeneous and dual-texture portions of the corresponding surfaces.

Selective separation of biological entities in microfluidic environment is an important task for a large number of bio-analytical protocols. Here we present a numerical study characterizing magnetophoretic split-flow thin (SPLITT) fractionation and compare its performance against field flow fractionation (FFF) in a microfluidic separation device. Particle trajectories in the microchannel under influence of a suitably designed magnetic field have been predicted by using an indigenous numerical code. A three-inlet and three-outlet micro-channel design configuration has been chosen for isolation of magnetic microspheres of two different sizes from a continuous flow. The configuration is chosen as a practicable option for simultaneous separation of two different biological entities from the background media. Parametric variation involving the particle size and relative widths of the outlet streams are carried out to observe the resulting influence on trajectories of magnetic beads and the particle capture and separation indices. Finally, an optimum regime of design parameter is identified that yields the maximum capture efficiency and separation index.

The vibration of droplets finds multiple applications in inkjet printing, combustion sprays, drop atomization etc. In many of these processes, the primary interest is to estimate the resonant frequencies and mode shapes of the vibrating drops. Previous works show extensive characterization of vibrating droplets in a gravity dominated regime, where Bond numbers (ratio of gravitational and surface tension effects) are greater than 2. In the present work, vibrations of small size droplets, in the capillary regime, with Bond number in the range 0.24–1.37 are considered on hydrophilic and hydrophobic surfaces. The surface of the vibrating drop at resonance is characterized using a novel interferometric method: Electronic Speckle Pattern Interferometry (ESPI) is explored. The resonant frequencies obtained through the interferometric patterns of ESPI is found to be in good agreement with a theoretical model considering a 1D capillary-gravity wave.

The aim of the present work is to conduct an evaluation of the ability of Single Relaxation Time (SRT) and Multi Relaxation Time (MRT) formulations of Lattice Boltzmann Method (LBM) to estimate permeability of a porous sample from numerical simulations in the pore scale. Fluid flow is simulated through digitized micro-tomographic images obtained using accurate imaging techniques. The dependence of the permeability calculated on the grid resolution, method used and the variable parameters in the method are studied. The mesoscopic nature of the LBM formulation facilitates the accurate computation of the property values from the pore scale simulation. However, it is observed that use of SRT LBM might not give a viscosity independent prediction of permeability due to numerical errors inherent in the method. Instead, the MRT LBM is found to give accurate predictions which are less dependent on viscosity with appropriately selected relaxation parameter matrix. Moreover, the effect of grid resolution selected on the accuracy of permeability values predicted is closely studied for both SRT and MRT. The conclusions obtained could be of use in predicting permeability for macroscopic flow calculations and realistic reconstruction of the pore geometry making these studies important from academic and industrial viewpoints.

A 3D fluid flow model was developed and used to study the effect of diffusion and geometric parameters on diffusion controlled drug delivery device in a capillary to mimic the in vivo behavior. It was observed that a desired release profile can be achieved by multiple strategies, e.g., a delayed release of the drug can be achieved either by increasing the size of the polymer coating or by changing the polymer coating so as to decrease the mutual diffusion coefficient of the drug in the polymer. The proposed model-based approach can be used to identify the relevant parameters, study their effects on the drug release and thus can be used in designing controlled drug delivery devices in a reverse engineering framework.

The present study looks at the aerodynamic load generation capability of a flapping type MAV subjected to fluctuating wind. MAVs are subjected to constantly changing operating conditions. The performance of flapping wing MAVs, under these conditions, have not been explored in great detail. Accordingly, this work investigates the performance of flapping wings in the presence of gusts. Towards this, pure plunging kinematics is chosen and the body is subjected to frontal gusts with sinusoidally modelled temporal variations. Thereafter, the airfoil response to variation of plunge kinematic parameters is studied in comparison with quasi-steady loads. A typical gust cycle is composed of many plunge cycles. The mean thrust produced in each of these plunge cycles vary throughout the gust cycle. This variation depends on the change in non-dimensional plunging velocity in the gust cycle. It is observed that a plunging airfoil is able to suppress variations in thrust due to sharp changes in non-dimensional plunging velocities.

The present work is focused on flow field behavior generated by rigid and flexible rectangular wings undergoing main flapping motion using two dimensional Particle Image Velocimetry (PIV). The experiments have been carried for an asymmetry one degree of freedom main flapping motion of both rigid and flexible low aspect ratio wings at 1 Hz flapping frequency in hovering flight mode (advanced ratio, J = 0) at zero geometric angle of attack, zero wing pitch angle and chord wise based Reynolds number of the order of 104 along the wings spanwise direction at its mid chord to obtain instantaneous flow fields. The improved understanding of effect of wake capture, observation of spanwise flow on the wing, and formation-growth-diffusion of wingtip vortices have been achieved. Effect of wing flexibility on the flow field has been studied by comparing the flow field of both rigid and flexible rectangular wings undergoing main flapping motion.

Blood flow hemodynamics plays an important role in the localized deformation of arterial lumen and progression of atherosclerosis. To understand the flow details, the present study examines the possibility of chaotic flow in rigid and compliant deformed tubes. The geometries selected mimic the diseased portion in a human body and the oscillatory flow conditions are similar to the vascular flow rates in terms of Reynolds and Womersley numbers. An experimental set up is established through a set of controlled solenoid valves to produce the required oscillatory waveform. The working fluid used is a mixture of glycerin and water. Three components of velocity are determined by recording an image sequence of particle motion using a two-camera system. The particle is density matched with the working fluid. Coordinates of the particle position and velocity are determined using the image sequences recorded by each camera. The overall approach to velocity measurement is similar to particle tracking velocimetry. The frequency of oscillation considered is 1.2 Hz. The experiment represents realistic blood flow conditions in the human aorta with Womersley number in the range of 10–12 while the Reynolds number is lower, being in the range of 500–800. Since particle motion is followed, it is possible to detect Lagrangian chaos in terms of the positive largest Lyapunov exponent. Results show that the Lyapunov exponent of a compliant model is slightly greater than that of the rigid. In addition, it increases uniformly with Reynolds number.

In this work, we investigate the aerodynamic characteristics and spatio-temporal dynamics of a wing cut section of dragon fly (Aeshna Cyanea) at ultra-low Reynolds number corresponding to the gliding flight of this dragon fly. The simulations employ an unstructured triangular mesh based on finite volume discretization. A critical assessment of the computed results is performed. Numerical simulations are performed at ultra-low Reynolds number of 10,000 at different angles of attack. Three insect wing sections are modelled with different orientation of the leading edge. It is shown that among all profiles, Profile LEU has largest gliding ratio at higher angles of attack. The larger gliding ratio is due to the fact that the overall drag coefficient is smaller as compared to other Profiles LES and LED. The smaller drag coefficient is due to the presence of large negative shear regions present in the flow. The negative shear regions are because of vortices formed attached to the leading edge or inside the pleats. The presence of vortices attached not only reduces the contribution of shear drag but pressure drag also.

Propulsive advantage in a three side-by-side (one above the other) arrangement as compared to single/isolated fish-like locomotion of a flexible hydrofoil is studied. A level set based immersed boundary method (LSIBM) is used for a transient 2D CFD simulation and analysis of hydrodynamics of fish like locomotion; modeled here by undulating NACA0012 hydrofoil. The study is undertaken for both antiphase and in-phase undulation (of the middle as compared to side foils) for various frequency (St = 0.4, 0.6 and 0.8) and gap ratios (d = 0.4, 0.6, 0.8 and 1), at a constant amplitude (A_max = 0.1), wavelength (λ = 1) and Reynolds number (Re = 400). Anti-phase as compared to in-phase undulation is found to give better propulsive performance. For side as well as middle hydrofoil, effect of frequency as compared to hydrofoil-spacing is found to be more dominant on the propulsive performance. Signature of thrust is shown with the help of momentum excess and reverse Von-Karman Street.

To resolve the problems of high emissions in CI engines, new combustion concepts have been recently developed. Premixed charge compression ignition (PCCI) combustion is a good example. It’s a strategy in which early injection is used causing a burning process in which the fuel burns in the premixed condition. In CI engines, PM and NO_X emissions are an extremely unsolved issue. PCCI is the promising solutions that combine the advantages of SI and CI modes of combustion. PCCI engine gives thermal efficiency close to the CI engines and resolves the problems of high NOx and PM simultaneously. Premixing of air and fuel preparation is the challenging part to achieve PCCI combustion. External mixture formation technique has been used to form premixed charge and for this purpose diesel vaporizer is device used to form diesel vapors. Low diesel fuel vapor volatility may be the obstacle in preparing premixed air–fuel mixture. Exhaust gas recirculation (EGR) can be used to control in-cylinder combustion temperature and the rate of heat release. The objective of this study is to improve thermal efficiency and reducing combustion noise and exhaust emission levels.

A high fidelity computational modelling of novel fire extinguisher designs is addressed in this work. The fire extinguisher works on the condensed aerosol particles acting as the fire extinguishing agent. The study is aimed at computationally predicting the various multi-species transport variables inside the extinguisher and the various critical temperature zone and regions in the extinguisher based on the computational results. The results computed here could serve as a basis for testing and certification for improvising the experimental design for the extinguisher and will provide the ways for the design cycle of the product.

The present study deals with the application of spectrometry in correlating flame colour with relevant equivalence ratios in the entire flammability limit, extending from lean blowout to rich blowout. A swirl-stabilized, LPG-fueled dump combustor was used for this purpose. The predominance of a specific colour at a particular equivalence ratio is noted viz. the predominance of red wavelength in richer regimes of operation, and that of blue wavelength in leaner regimes. The practical application of blow out prediction is significant in the gas-turbine industry. The salient contribution from the present study is the development of prediction parameters for both lean and rich blow out at low flow rates. Apart from spectrometric analysis, an attempt has also been made to predict RGB-intensity values using image processing tools.

Reacting flow simulation of high area ratio rocket nozzles is done using an indigenously developed Point Implicit Unstructured Finite Volume Solver. A numerical solution procedure to solve turbulent-reacting nozzle flow field is developed, which is based on the implicit treatment of chemical source terms by preconditioning and then explicitly solved along with unsteady turbulent Navier-Stokes equations. Chemical equilibrium was assumed in the nozzle inlet and the properties of combustion products and species concentration resulting in thrust chamber are obtained using chemical equilibrium composition code. Using this equilibrium composition as boundary conditions at inlet and ambient pressure conditions at exit, the present turbulent—reacting flow solver was able to successfully simulate nozzle flow field and predicted the delivered specific impulse.

Energy consumption has increased steadily due to industrialization and rise in population of the world. Fossil fuel, especially crude oil, is the predominant energy source around the globe. However, the reserves of fossil fuel are limited and will be depleted in near future. Therefore, there is a great interest in exploring alternative renewable energy. Biogas, a renewable fuel, can be used in internal combustion engines for power generation. The utilization of biogas in diesel engines in dual fuel mode has colossal prospective if explored to the fullest. The current investigation unravels the influence of load level on the performance and emission characteristics of a biogas powered dual fuel diesel engine at different compression ratios. Results revealed that the performance and emission of a biogas powered dual fuel diesel engine improves at high load level. However, CO, CO₂, HC, NO_X emission and cylinder pressure increases at high load level.

The small residence time, in designing the engine of a supersonic aircraft, presumed to have a very important character in combustion. At hypersonic flight, the flow is supersonic while entering in the combustor to avoid excessive heating and fuel is essentially to be injected, mixed and combusted entirely within a short residence time of the order of millisecond. In order to resolve the restrictions given by short residence time, numerous studies have been carried out to suggest the concepts of injection, among which, the transverse fuel injection in a combustor with a cavity is being used in several engines. This paper describes the numerical study of the combustion enhancement with hydrogen fuel injection in a transverse aperture nozzle into a supersonic hot air stream. Several cavities with single and dual steps with different cavity wall angles are analyzed. Eddy dissipation concept model with detailed hydrogen-air combustion with 21 reactions and 9 species transport has been applied to numerically simulate the reacting flow of hydrogen fuel scramjet combustor. The mixing enhancement, static pressure and combustion efficiencies are analyzed for different cavity geometries.

It is well known fact that diesel engines are commonly used for transportation and power generation due to their high efficiency, low fuel consumption and durability. On contrary these engines churn out harmful and hazardous emissions like particulate matter (PM) and nitrogen oxides (NO_x). Recently Bio-origin renewable fuels have taken center stage of discussion because of their ability to replace depleting fossil fuels and capacity to reduce hazardous engine exhausts emissions when used in diesel engines. In the present experimental study Simarouba glauca biodiesel is used in a naturally aspirated four stroke single cylinder air cooled direct injection kirloskar DA10 engine. The main objective is to investigate the effect of biodiesel and exhaust gas recirculation (EGR) on the performance and emission characteristics of a CI engine at 180 bar fuel injection pressure (FIP) with standard injection timing. B20, B40 biodiesel blends with 10, 15 and 20 % EGR ratios were used for the study to investigate brake thermal efficiency (BTE), carbon monoxide (CO), unburned hydrocarbons (UBHC), NO_x, and smoke opacity. Reduction in CO, HC and smoke opacity is noticed with simarouba biodiesel fuel while increasing NO_x compared to diesel. Application of EGR along with biodiesel resulted in simultaneous reduction of nitrogen oxides and smoke without affecting engine performance. It was found from experiment that B20 blend at 15 % EGR shown superior performance characteristics compared to other conditions.

Heat treatment of metal is an energy intensive process. Currently direct electrical energy is employed for this purpose. The harnessed heat using concentrated solar thermal technology can be employed for processing of metal, like, annealing of Aluminium. This paper presents a technology that uses solar energy as fuel and converts the harnessed heat for this purpose. An existing heat treatment furnace is scaled down and retrofitted to demonstrate solar convective heating concept. Air-flow velocity measurements in furnace side-duct are performed using laser Doppler velocimeter (LDV) along the centerline of injection circular nozzle. Comparison with the reported impinging jet profiles shows that air-flow in the side-duct is asymmetric. Computational fluid dynamics (CFD) approach based on different turbulent models is used for air-flow analysis. The selected CFD approach is validated by comparing measured velocities. Validated CFD tool is used for details flow analysis in the furnace. Detailed analysis revealed the formation of a vortex structure under the heart region, which is expected to influence the metal processing quality.

Dielectric barrier discharge (DBD) plasma actuator is a promising flow control device for enhancing the performance of various energy systems. A DBD plasma actuator is initiated by the application of high frequency O (kHz) and high AC voltage O (kV). In this paper, a new design of DBD actuator with variable dielectric thickness has been proposed and compared with the standard actuator on the basis of body force, induced velocity and length of DBD plasma wall jet. The dynamics of flow generated by the actuator was visualized and starting vortex [1] development was captured by a Z-type schlieren technique.

Electro-encapsulation is an emerging technology to encapsulate of micro/nano particles with very high encapsulation efficiency and a broader size distribution of capsules in single step. The present study experimentally examines electro encapsulation of a immiscible liquid pair. We have used ethylene glycol-olive oil as a liquid pair for this analysis. The effect of different physical and operational properties of inner and outer liquid is examined. Nondimensional approach is used to explain the experimental results as a function of different dimensionless number viz. Electrical Bond no (Bo_e), Masuda no (Md), and Capillary number (Ca).

In the present work we numerically investigate the oscillations of a sessile conducting droplet in the contact and non-contact modes under an alternating electric field. We show that the oscillations in the non-contact mode, where the needle electrode remains away from the drop, are caused by the electric forces due to charge accumulation at the apex of the drop. In the contact mode case, where the needle remains dipped inside the drop, the electric charge accumulates at the drop surface just above the dielectric coating with a maximum value near the three phase contact line. These charges push the three phase contact line outwards with an oscillatory force which leads to drop oscillations. We also observe that higher needle voltage (~1 kV) is required for the non-contact mode while considerably less potential (~10 V) is enough for the contact mode to cause drop oscillations.

The problem of steady, laminar flow of an incompressible and electrically conducting fluid with mixed convection over a circular cylinder subject to uniform surface temperature is considered. The cylinder is placed to approaching flow stream for normal (cross flow) direction to the buoyant force and an external magnetic field is applied in the direction opposite to the fluid flow. The governing Navier-Stokes equations with energy equation are solved by using higher compact finite difference scheme in 2D cylindrical polar coordinates. Numerical solutions with temperature fields were obtained for Reynolds number Re = 20, Prandtl number (0.065 ≤ Pr ≤ 7), Richardson number (0 ≤ Ri ≤ 2) and magnetic field (0 ≤ N ≤ 4). The results obtained are plotted in the form of contours of streamlines and isotherms. The flow and temperature fields are presented and the results are discussed.

Ferrofluids are colloidal suspensions of single domain superparamagnetic nanoparticles, typically of the order of 10 nm in diameter, in nonmagnetic liquids. In absence of an external magnetic field the fluid does not show any magnetic behavior due to random thermal Brownian motion of the magnetic nanoparticles. However, the fluid bulk exhibits magnetic polarization when exposed to a magnetic field. Temperature-sensitive magnetic fluid experiences a change in magnetic susceptibility as its temperature changes. Under combined influence of external magnetic and temperature field gradients, a Kelvin body force is established in a ferrofluid bulk such that the high temperature ferrofluid is repelled away and colder ferrofluid is attracted towards the region of stronger magnetic field. This thermomagnetic advection causes enhanced convective heat transfer in ferrofluids. Herein a numerical study of thermomagnetic convection in a rectangular annulus (formed by placing a solid block inside a larger enclosure) is presented. Magnetic field is created by a series of small permanent magnets in a regular or a Halbach array. Heat transfer characteristics under different thermal and magnetic arrangements are presented. The configuration is suitable for a host of engineering applications, e.g., electronics cooling or ferrofluid-based solar thermal or a thermomagnetic energy conversion loop.

A meshfree framework for numerical simulations of magnetohydrodynamic flows is proposed. The framework is based on the Least-Squares-Based Upwind Finite Difference method (LSFD-U) and is capable of handling arbitrary point distributions. The approach is based on the least-squares method of error minimisation to compute the inviscid flux derivatives. The flux derivatives at every point require the fluxes at the point as well as those in fictitious interfaces in a neighbourhood around it. The fluxes at the fictitious interfaces are computed by using any numerical flux formula of interest that incorporates upwinding and consequently a global rather than the one-sided stencil may be chosen for computation. The meshfree framework is implemented through AUSM scheme, using a first-order accurate spatial and temporal discretisation. Studies on the one-dimensional MHD shock tube problems demonstrate the efficacy of the algorithm. The effect of non-uniform point distributions on the performance of the meshfree framework particularly with regard to conservation has also been studied. On the non-uniform grid the solutions of meshfree framework are not in agreement with the solutions of the finite volume framework unlike on uniform meshes. The finite volume formulation is known to be conservative and therefore it is very clear that meshfree formulation has conservation issues particularly as the grid becomes more non-uniform. It is therefore desirable to have a formulation for meshfree framework that preserves conservation at a discrete level like the finite volume method. Attempts have been made to develop a conservative meshfree framework using weighted least-squares technique for a particular case of one-dimensional non-uniform point distribution.

Pneumatic transport is one of the most widely used methods for the carrying solid particles in process industries; however, the process is energy intensive as the instability in the conveying line sets in at a volume fraction much lower than 0.1. The typical Zenz plot for a pneumatic conveying system shows that there exists a minima in the line pressure drop versus superficial gas velocity plot and the regime immediate to the left of the minima is identified as “unstable”, as a large fluctuation in pressure drop is observed in this operating regime. A recent investigation shows that the fluctuation of the line pressure drop is accompanied by formation and recede of distinct dunes in the transport line. Formation of dunes, though studied extensively in the context of geophysical flows, is less emphasized in the literature of pneumatic conveying. The objective of the present work is to investigate the formation of dunes in the horizontal pneumatic conveying system and to propose a possible phase diagram to demarcate the operating regime where distinct, stable dunes are formed. To that end, a variable length pneumatic transport system is fabricated. The conveying line is made of transparent glass tubes for clear visualization of the test section. High speed images with good resolution are captured to study the dynamics and the morphology of the dunes formed. Single and multiple distinct, equidistant dunes are observed to form in the conveying line. A phase diagram on the ṁ _s –ṁ _a plane, where, ṁ _s and ṁ _a are the mass flow rate of the solid and the fluid phases respectively, is proposed to classify the different flow regimes of a horizontal pneumatic transport system.

The inelastic collision between the grains renders the flow of granular material through a silo complex and gives rise to various pattern formations. A detailed qualitative observation of granular flow through a two-dimensional rectangular flat bottomed silo is presented for concentric and eccentric discharge. The free surface slides down towards the centre of opening and makes an angle which is very close to the angle of repose of the particles. The free surface becomes ‘V’ shaped for the concentric discharge and linearly inclined for eccentric discharge.

A natural circulation loop (NCL) consists of a heat source at lower elevation, heat sink at higher elevation and connecting piping. It is representative of primary heat transport system of a nuclear reactor or a solar power plant. The study of steady state and transient characteristics of the NCL is hence important. In this work, a 1D simulation code is developed to model the NCL. The effect of heater power on steady state mass flow rate and temperature rise across heater is studied and compared with experimental data for validation. Further, the code is applied to obtain the flow initiation transients of various configurations of the NCL.

In the present work an entropy generation analysis is carried out for a solid nuclear fuel element surrounded by flow of coolant through a concentric annular passage. In present system we considered uniform heat generation from the solid fuel core and steady state conditions where the fuel-clad gap is filled with helium gas only. A conjugate approach is adapted in the entropy generation analysis, where the effect of solid core heat generation and the temperature gradients inside solid core, gap and cladding are considered as well along with the irreversibilities arising out of fluid flow. The effect of Reynolds number, duty parameters and diameter ratio on overall entropy generation has been investigated in details for turbulent flow regime. For a certain ranges of duty parameters and diameter ratio, the optimal flow conditions are found from the analysis.

In the present study, an experimental investigation has been carried out to analyze the effect of surfactant on heat transfer characteristics of a circular impinging liquid jet. A rectangular stainless steel foil (AISI-304, 0.15 mm thick), used as the target surface, was electrically heated to obtain the required initial temperature. A single-phase circular water jet of diameter 1.38 mm is allowed to impinge on the hot surface. Thermal images of the target surface during liquid jet impingement were recorded by using an infrared camera (A655sc, FLIR System) positioned on the side of the target surface opposite to the impinging nozzle. The distribution of heat flux on the target surface is evaluated from the recorded thermal images during transient cooling. Tests were performed for an initial surface temperature of 500 °C, Reynolds number (8893 ≤ Re ≤ 12847) and nozzle to plate distance was l/d = 2.5. Experiments have been performed using 2-Ethyl Hexanol added water solution at different concentration (0–400 ppm). Surface heat flux distribution during transient cooling of hot surface is obtained. It was observed that the surface heat flux increases with the rise in the jet Reynolds number and achieves its maximum at surfactant concentration of 200 ppm at stagnation point (6.2 MW/m2 at Re = 8893 to 6.5 MW/m2 at Re = 12847; 200 ppm).

Jet impingement cooling has been studied extensively as this finds applications in the areas of reactor safety, electronic cooling etc. In practical applications, orthogonal jet impingement is a very ideal situation and the jet may hit the surface at some angle causing local uneven Nusselt number distribution over the surface. In this numerical study, 3-D simulations are carried out in Fluent 14.0 to investigate the effect of Reynolds number, distance between nozzle exit and the plate on the heat transfer characteristics. Standard κ-ε with standard wall functions and enhanced wall functions, SST κ-ω, Standard κ-ω, V2F turbulence models have been studied for orthogonal jet impingement in this work. This study has been extended to inclined jet impingement. At jet plate spacing of Z/d ≤ 0.5, SST κ-ω turbulence model predicts Nusselt number variation satisfactorily while for Z/d ≥ 0.5 V2F turbulence model is best suited. In this work, jet plate spacing of Z/d = 2, Reynolds number of 28000 and 40000 has been studied. At small jet plate spacing and inclined jet impingement, the flow behavior over the plate changes. Profile of constant Nusselt number elongates along the downhill side of the plate. Contours of high Nusselt number compresses towards uphill side of the plate. Maximum heat transfer rate is from the downhill side of the plate and location of point of maximum heat transfer shifts towards “uphill” side of the plate. This shift in point of maximum heat transfer depends on “angle of jet impingement”.

Jet impingement cooling has been studied extensively as this finds applications in the areas of reactor safety, electronic cooling etc. The convective heat transfer process between the circular air jet impingement on uniformly heated flat plate is studied numerically. In this numerical study, 3-D simulations are carried out in Fluent 14.5 to investigate the effect of Reynolds number, distance between nozzle exit and the plate on the heat transfer characteristics. Standard κ-ε, SST κ-ω, Standard κ-ω, V2F turbulence models have been studied for orthogonal jet impingement in this work. For Z/d ≥ 0.5, V2F model is best suited. Reynolds number of 12000, 20000, and 28000 has been studied. A typical feature of circular air jet impingement at low jet plate spacing is occurrence of secondary peak in Nusselt number variation along radial direction over the plate. V2F model correctly predicts the secondary peak in Nusselt number variation over the plate. Other models fail to predict the secondary peak which is of significant importance in air jet impingement at low jet-plate spacing. V2F model do not use wall functions. A fine grid at the surface of the wall is necessary to capture the flow behavior near the wall.

In nuclear reactor containment, Sump, Calandria Vault and Calandria Vessel contain large amounts of water. Condensation on walls and containment spray system actuation also results in accumulation of water in the containment sump during the accident conditions. Evaporation of water takes place during the accident conditions and needs to be accounted in the hydrogen distribution analysis. Lump parameter codes such as ASTEC have built-in models for sump water evaporation. However, CFD codes are being increasingly used for containment hydrogen distribution studies, development of a sump water evaporation model for multi-dimensional calculations is required. The sump model is implemented through mass and energy balance using two different approaches. The main focus of the paper is on the simulation of sump evaporation experiment conducted in TOSQAN facility using the lumped parameter code and its comparison with the CFD results and the available experimental data.