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About this book

This book presents a collection of the best papers from the Seventh Asian Joint Workshop on Thermophysics and Fluid Science (AJWTF7 2018), which was held in Trivandrum, India, in November 2018. The papers highlight research outputs from India, China, Japan, Korea and Bangladesh, and many of them report on collaborative efforts by researchers from these countries. The topics covered include Aero-Acoustics, Aerodynamics, Aerospace Engineering, Bio-Fluidics, Combustion, Flow Measurement, Control and Instrumentation, Fluid Dynamics, Heat and Mass Transfer, Thermodynamics, Mixing and Chemically Reacting Flows, Multiphase Flows, Micro/Nano Flows, Noise/NOx/SOx Reduction, Propulsion, Transonic and Supersonic Flows, and Turbomachinery. The book is one of the first on the topic to gather contributions from some of the leading countries in Asia. Given its scope, it will benefit researchers and students working on research problems in the thermal and fluid sciences.

Table of Contents

Frontmatter

Effect of Coaxial Airstream on High-Pressure Submerged Water Jet

The effect of coaxial airstream on a high-pressure water jet is studied by measuring the stagnation pressure on the impinging target and by the optical observations of the water jets. The water jet is pressurized at 12.7 MPa and discharged into atmosphere and still water, which correspond to non-submerged and submerged water jets. The coaxial air is also pressurized at various pressure po/pb = 1.0–3.0, where po and pb are the stagnation air pressure and the atmospheric pressure. And the distance between the water jet nozzle and the normal target plate L divided by the nozzle diameter D is changed from 1.0 to 15. As a result, according to the optical observation for non-submerged case, the spreading angle of the non-submerged water jet is found to be the minimum angle in case of the coaxial air jet pressure ratio of 1.4. The recovery factor decreases both for the case of non-submerged and submerged one decrease as L/D increases. However, the recovery factor in case of submerged water jet is greatly increased by the coaxial airflow by 70% of that for no airstream. Comparison of the recovery factors between the case of submerged and non-submerged conditions reveals that the coaxial airstream seems to achieve the atmospheric environment for the submerged water jet, even in the submerged conditions.

Minoru Yaga, T. Wakuta, R. V. Reji, Heuy Dong Kim

Heat Transport Evaluation of Nanosuspension as Latent Heat Storage Material

This paper deals with the characteristics of a straight pipe inner flow of the nanosuspension that has non-Newtonian viscosity. The parameters are set in the mass composition of 10–20 mass% of dispersoid and in the temperature range of 20–70 ℃ that includes the melting point of tetracosane. The experimental study is carried out by using the flow pressure loss measurement apparatus. The test section that made of a stainless straight pipe has an inner diameter 8 mm, and it has the length 1000 mm. The inner flow of a straight pipe is occurred by using a pump that is controlled by an inverter. The pressure drop is measured by a differential pressure gauge. The measured pressure loss is used for the calculation of the flow friction loss coefficient and the pump power. The experimental data are evaluated by the variation of the pressure loss coefficient with Reynolds number that defined by the non-Newtonian behavior. Viscosity data by previous study data that correlated by the power law method are used for Reynolds number calculation. The viscosity including non-Newtonian characteristics had been estimated by using a rotary viscosity meter. The measuring ranges are shear rate <500 1/s and temperature 10–84 ℃. The calculation data from experimental correlation equation, which was adjusted by an exponential law, are used for Reynold’s number. The flow friction loss coefficient and the pump power are estimated by measured flow pressure loss. The heat transport amount is calculated by the sensible heat and the latent heat of nanosuspension. The thermal property data (specific heat and latent heat) are the obtained data by previous study that measured by using differential scanning calorimeter. The relationship between the heat transport amount and pump power of this study is shown that the heat transport ability of nanosuspension is 1.5–2 times of water at the same value of pump power.

Shin-ichi Morita, Taiki Ito, Yasutaka Hayamizu, Takanobu Yamada, Akihiko Horibe

Development of a Flight Stage Command System Pressure Regulator and Modeling Using LMS IMAGINE AMESIM

Command system is an integral part of any flight or ground test stage of a launch vehicle. High pressure command gas is stored in gas bottles at either ambient or cryogenic temperatures and then expanded using single or multi-stage pressure regulation system. Prediction of pressure regulator behavior during transient and steady state is of great importance. There had been many efforts earlier to predict pressure regulator behavior using governing differential equations and solving them by either numerical techniques or standard MATLAB/FORTRAN commands, but stability and performance of these models are highly dependent on various factors like friction coefficients, damping, inertia and real gas behavior, etc. The ability and accuracy of modeling tools for prediction of system dynamics and its behavior at various operating conditions have increased to a greater extent and becoming extremely popular these days. This paper presents a dynamic model, generated using LMS IMAGINE AMESIM as a modeling tool. This model is used for generating and optimizing various design parameters, i.e., Coulomb friction, size of damping orifice, reference spring load, biased spring load and inertia of moving parts, etc. Dynamic model is generated using standard modules available in software library, and each sub-module represents either a pneumatic chamber or a physical phenomenon like inertia of moving elements, friction and/or inherent damping of the system. Design parameters thus generated are then utilized to develop an actual flight worthy pressure regulator. Comparison of simulation results with actual hardware test results shows a close match during the transients and in steady phase. A series of tests including flow and slam tests were conducted and the performance of pressure regulator is captured using continuous data acquisition system on various hardware’s and a comparison of results is also presented here. Parametric study on regulator stability by varying various system parameters is also conducted. The model is found to be very helpful in understanding behavior of flight stage command system pressure regulator and can be further utilized to generate system-level models. It can also be utilized in understanding behavior of pressure regulators in series and parallel, which is otherwise very complicated. An extension to this model can be a plausible system-level model, which will further augment understanding of entire command system and also unravel many system related queries.

Gaurav Sharma, S. Sunil, D. Venkittaraman, M. Radhakrishnan

DSC Analysis of Nano-enhanced Monobasic and Binary Solid-Solid Phase Change Materials for Thermal Storage

Solid-Solid PCMs are latent energy storage substance that can absorb, store and release a substantial amount of thermal energy. Since polyalcohols have low thermal properties, nanoparticles are added to enhance these properties. In this study solid-solid NPG, TAM and binary PCM along with different mass percentage (0.1%, 0.5% and 1%) of aluminium oxide (Al2O3) nanoparticle is evenly dispersed using a low energy ball mill. DCS tests were performed on each sample at 10 ℃/min heating rate to investigate its thermal properties. It can be observed that the addition of nanoparticles tends negligible effect on transition temperature and latent heat of enthalpy. The transition temperatures for NPG, TAM and binary PCMs before thermal cycling were 51.86 ℃, 138.5 ℃ and 45.76 ℃, respectively. Also, no significant changes were observed for transition temperatures after thermal cycling.

K. P. Venkitaraj, S. Suresh, B. S. Bibin, Jisa Abraham

A Novel Arrangement of Rectangular Fins for the Enhancement of Heat Transfer in a Rectangular Duct

Efficient harvesting of renewable energy such as solar, wind and wave is crucial at present times to meet the increasing demand for the energy in India. Solar air heaters (SAH) which convert solar energy into useful thermal energy for the industrial and agricultural purposes show lower efficiency, inherently due to the low thermal conductivity of the air which results in lesser heat transfer between absorber plate and air. In this paper, we investigate the effect of inclined rectangular fins on the fluid flow and heat transfer inside a rectangular duct SAH. The fins are arranged in such a way that they form a series of converging and diverging passages. The fin height is fixed at half of channel height. Two types of designs are considered: Type 1 (with a 2:1 convergence ratio) and Type 2 (with a 4:1 convergence ratio). CFD analysis is performed by using ANSYS software for both designs with 3, 4, 5, 6 and 7 rows of fins, at Reynolds numbers 4000, 8000, 12,000 and 16,000. The efficiency of the fin is quantified by using dimensionless parameter thermo-hydraulic performance parameter (THPP). The results show that the converging and diverging passages induce swirl in the fluid, which helps in enhancing heat transfer with little increase in friction loses. The swirl flow sustains longer for Type 2 design with higher convergence ratio, thus requiring lesser number of rows of fins compared with Type 1 for the better performance. Also, it is observed that overall the Type 2 arrangement gives higher THPP compared to the Type 1 arrangement with the highest THPP of 1.588 for 5 rows of fins at Reynolds number 8000.

Dolfred Vijay Fernandes, Soham Parija, Dushyant Singh Khinchi

Generation of Extra Shock Wave Over a Half Wedge in a Supersonic Flow

Supersonic flow at Mach number 2.0 is simulated over a half wedge using ANSYS CFD software for both viscous and inviscid flows. The formation of extra shock wave at the leading edge below the wedge is observed from the results of viscous analysis which supports previous research observations. Generation of this extra shock wave is further investigated using time-dependent numerical simulations. Boundary layer formation and the shock wave generation over the lower surface of the half wedge are studied from the unsteady analysis. From this study, it is investigated whether the formation of the boundary layer and the generation of the extra shock wave are interdependent. Time-dependent results showed that the formation of the boundary layer and the generation of extra shock wave are independent of each other.

Chera Rajan, Rajarshi Das, Heuy Dong Kim

Numerical Study of Effect of a Wire Mesh on Fluid Depletion Characteristics of a Cryogenic Propellant Tank

A new generation launch vehicle developed by ISRO consists of solid, liquid, and cryogenic stages. Cryogenic stage uses liquid oxygen and liquid hydrogen as oxidizer and fuel, respectively, for propulsion. Fuel and oxidizer are stored in cylindrical tanks with tori-spherical end domes. When the above fluids get depleted from the tanks, dip formation in the liquid surface and subsequent ullage gas entry into the outlet occurs. Formation of surface dip and subsequent gas entry into the outlet is governed by either sink potential phenomenon or vortex phenomenon or combination of both. This could lead to malfunction of the liquid rocket engine. Critical height of propellant from the tank bottom is defined as the elevation at which surface dip forms. Hence, the estimation of critical height is very important in order to quantify unused propellant toward the end of the thrusting phase. Two-phase flow due to vortex can be eliminated by providing either anti-vortex baffle or wire mesh/filter. But it cannot be eliminated due to sink phenomenon unless the outlet is properly designed. Oxidizer tank is provided with a siphoning feed line with wire mesh on the upstream of the inlet to supply contaminant-free liquid oxygen to engine. Published literature on siphoning feed line for the estimation of critical height is very limited. In addition to the above, information on effect of pressure drop due to the presence of wire mesh in the flow path on critical height is also not available. Numerical analysis is carried out using ANSYS CFD software to estimate the critical height for the above siphoning feed line with wire mesh. In order to verify the modeling of wire mesh, two different fluid models (without wire mesh and with wire mesh having zero pressure drop) are used. Oxidizer and gas contained in the tank are idealized as incompressible viscous fluids. Time-dependent Reynolds Averaged Navier Stokes (RANS) equations with continuity and volume fraction equations are solved to estimate the height at which surface dip forms. Numerical simulations are repeated using the fluid model with wire mesh for different pressure drops across it in order to find its effect on critical height. Pressure drop across a wire mesh is due to reduced flow area and is dependent on wire mesh size, density, viscosity, and velocity of fluid. From the numerical investigations, it is found that the presence of wire mesh in the flow path at the upstream of siphoning feed line results in higher critical height due to pressure drop across it. Hence, it is recommended to relocate the wire mesh to the inlet of the siphoning feed line. Another important conclusion is that radial velocity at the inlet of siphoning feed line should be low so that the liquid till its inlet can be utilized. This can be achieved by increasing the bell mouth diameter of the siphoning feed line.

Srinivas Kodati, Suresh Mathew Thomas, A. K. Asraff, R. Muthukumar

Fetal Congenital Heart Disease Detection Using Echo Image Enhancement of Atrio-Ventricles (AV) and Vascular Blood Flow

Nowadays, digital image processing technology has got vast application in the field of biomedical engineering. In this paper, we introduce a software solution for the echo image enhancement of atrio-ventricular and vascular blood flow for the detection of fetal congenital heart disease (CHD). The proposed method provides a 2D representation of the fetal heart from ultrasound images. The ultrasound images undergo different processes such as de-noising, segmentation, and enhancement so that CHD can be accurately detected if present. After the segmentation, fetal echo image will clearly distinguish the right atrium-ventricle and left atrium-ventricle blood flow. The proposed image enhancement techniques will help even for a less skilled radiologist to detect and identify the CHD from the fetal echo images.

Praveen Prasannan, K. S. Biju, R. Prasannakumar

Numerical Analysis of Regular and Irregular Surface Roughness in a Microchannel Using LBM

To investigate the thermal and hydrodynamic behaviors in a rough microchannel, the alternative arrangement of mixing triangular and rectangular ribs for regular and irregular spaced and heights has been considered using thermal lattice Boltzmann method (TLBM). The TLBM is a kinetic method based on the particle distribution function, so it can successfully be implemented to study the flow dependence on Knudsen number including slip velocity, pressure drop in rough microchannel. The friction coefficients in terms of Poiseuille number (Pn) and the rate of heat transfer in terms of Nusselt number (Nu) have been discussed in order to study the effect of surface roughness geometries in the slip flow regime at Knudsen number (Kn), ranging from 0.01 to 0.10. It was found that the effect of surface roughness is more pronounced at low Knudsen numbers as well as random spaced and heights. Finally, the thermo-hydraulic performances have been discussed for various cases numerically and the results are compared with the smooth microchannel.

M. A. Taher, M. K. Dey, Yeonwon Lee

Numerical Study on the Behavior of an Elastic Capsule in Channel Flow Using Immersed Boundary Method

The study of motion and dynamic behavior of elastic capsules in Poiseuille flow in a channel has become an interesting topic of research because of the wide range of applications in the field of biomedical engineering. The behavior of an elastic capsule in an externally applied flow is challenging because of the large displacement fluid–elastic structure interaction involved. In this work, we develop a computational model to capture the physics of the motion and behavior of an elastic capsule in Poiseuille flow in a channel using an immersed boundary finite volume method. The circular-shaped capsule is divided into a number of immersed boundary (IB) points. We create elastic links structure between IB points to incorporate tension/compression and bending. The flow is governed by continuity and Navier–Stokes equations which are discretized using staggered grid-based finite volume method. Dirac delta function is used to interpolate between solid (capsule) and fluid grids. Simulations are first carried out to describe the instantaneous position and shape of the capsule at a fixed Reynolds number flow in the channel. It is observed that the initial location has a significant influence in determining the final shape and position of the capsule. Further, through numerical simulations, the position and shapes of circular capsule in center-line motion with different stiffness constants for links are obtained and compared. It is found that lower elastic spring constant together with lower bending stiffness constant leads to larger deformation of the capsule because of less resistance to the flow. Also, the outcome of different Reynolds numbers (Re) on the behavior of the capsule is investigated for the center-line motion. It is noticed that the motion of the capsule retards with the increase in Reynolds number. Also, for higher value of Re, the capsule deforms less. For lower value of Re, the capsule deforms to a large extent.

Ranjith Maniyeri, Sangmo Kang

Characteristics of Underexpanded Supersonic Impinging Jet Caused by Rectangular Nozzle

The interaction between the supersonic jet and an obstacle is one of the fundamental problems of the compressible fluid dynamics and causes various problems of the aeronautical and other engineering, such as the design of a rocket launcher system. The many studies had been carried out for the interaction between the circular jet and an obstacle. It seems that the characteristic of the interaction between the rectangular jet and an obstacle is necessary to clarify and to control the interacting jet, but it is not conducted many investigations into the characteristic of a rectangular jet. This paper aims to clarify the characteristic of the interaction between the rectangular jet and an obstacle by the experiment and the numerical analysis.

Tsuyoshi Yasunobu, Xin Jiang, Kairi Komatani, Yuta Fujiwara

A Numerical Study on Planar Nozzles with Different Divergence Angles

Rocket nozzles accelerate combustion products or high-pressure gases to supersonic velocities. The planar nozzle is a type of conical nozzle, having a rectangular cross section. At low altitude, the ambient pressure is higher than the exiting jet pressure which leads to flow separation from the nozzle wall. In planar nozzles, asymmetric flow separation can be observed at low nozzle pressure ratios. Asymmetric flow separation can lead to undesirable side forces. In the present study, numerical analysis is performed on the flow-through planar nozzles. Nozzle geometries with different divergence angles and same area ratio are considered, and flow analysis is performed using commercial software ANSYS Fluent. All geometries are studied with similar boundary conditions. The numerical analysis is done on 2-D planar models. Reynolds-averaged Navier–Stokes equations are solved with realizable k-ε turbulence model. For the validation of the planar nozzle, flow features and wall pressure along the length of the nozzle are taken for different nozzle pressure ratios (NPRs) for 5.7° planar nozzle. It is found that as divergence angle increases magnitude of side load decreases and flow becomes symmetry at low NPR.

Prasanth P. Nair, Abhilash Suryan, Renju Chandran

Dynamics of Flexible Filament in Viscous Oscillating Flow

The dynamics of flexible filament in a viscous fluid is a complex fluid–structure interaction problem that has wide scientific and engineering applications in emerging fields such as biomimetics and biotechnology. Coupling the structural equations with fluid flow poses a number of challenges for numerical simulation. In this regard, techniques like immersed boundary method (IBM) have been quite successful. In the present study, a two-dimensional numerical simulation of flexible filament in a rectangular channel with an oscillating fluid flow at low Reynolds number is carried out using IBM. The discretization of governing continuity and Navier–Stokes equation is done by finite volume method on a staggered Cartesian grid. SIMPLE algorithm is used to solve fluid velocity and pressure terms. The filament mechanical properties like stiffness and bending rigidity are incorporated into the governing equation via Eulerian forcing term. An oscillating pressure gradient drives the fluid while the flexible filament is fixed to the bottom channel wall. The simulation results are validated with filament dynamic studies of previous researchers. The interaction of the filament with nearby oscillating fluid motion is well captured by the developed numerical model.

Mithun Kanchan, Ranjith Maniyeri

Numerical Investigation on Effects of Profiled Endwall Over Purge Flow in Linear Turbine Cascade

This paper describes the combined effects of purge flow and non-axisymmetric endwall profiling on the aerothermal performance of a linear turbine cascade. Purge slot with 45° ejection angle and three different endwall profiles, with varying hump to dip height, are analyzed. Performance of profiled endwall is compared with the non-profiled case. Reynolds-averaged Navier–Stokes (RANS) equation with SST turbulence model is used for numerical simulation. The analyzed results explore the demerits of current endwall profiles and how the transverse movement of weaker boundary layer fluid from the hub-pressure side corner enhanced. Compared to base case, endwall profiling enhanced the overturning and secondary flow kinetic energy at cascade exit. Apart from this, the profiled cases are providing very effective endwall protection compared to non-profiled purge case.

Sushanlal Babu, K. N. Kiran, J. K. Tom, S. Anish

Experimental Study on Temperature Profile Within a Compressed Air Tank

The study on temperature profile of compressed gases in a storage medium is of significance to many applications. Compression of gases is accompanied by a rise in temperature. The temperature varies at various coordinates within the chamber. In the case of inflammable gases the maximum temperature attained inside the chamber should not exceed its flashpoint, and it should be kept to an optimum value which is safe. In the present study, an experimental assessment is conducted on the temperature profile within a high-pressure tank being filled with air. An array of thermocouples arranged in tree form is utilized to capture the temperature profile accurately. The output is continuously monitored and stored using data acquisition system and LabVIEW. It is observed that the ambient temperature during the filling process has significant effects on the filling behavior in general and in particular on the final in-cylinder temperature and filled mass of gas.

Albin Mathew, V. Arjun, Manu Prasad, A. V. Vishnu, Sandeep Soman, Abhilash Suryan

A Study on Vortex Occurring in Jet Boundary of Underexpanded Jet

This study discusses an advective velocity of vortex occurring in the field near jet boundary of an underexpanded jet. The underexpanded jet is well known as one of the supersonic jet and it is formed when the pressure ratio across a convergent nozzle, from which the jet is exhausted, is more than the critical value. Owning to outstanding physical characteristics of the underexpanded jet, it has been used in many fields, such as laser cutting, exhaust jet of rocket and cooling process of tempered glass. However, the jet is not uniform and has typical cell structure because the expansion wave, the compression wave and the shock wave are periodically formed in it. Furthermore, vortices are induced in the flow field due to shearing stress generated along the jet boundary. And they interact with shock wave at a cell node of jet, which is closely related to a noise radiating from the jet. In the experiment, a convergent nozzle was used. The nozzle pressure ratio was changed, and the flow field was visualized using optical techniques such as Schlieren method. A number of photographs were taken at random under each condition and a structure of the flow field was examined. And the acoustic noise emitted from the flow field is measured using a microphone. Furthermore, the motion of vortex near the jet boundary was measured using a device composed of a laser and a photo-electric sensor such as a simple Schlieren system. Finally, from these results, the advective velocity of vortex was investigated. The results showed that the oscillation mode of the jet is changed from axisymmetric to lateral as the pressure ratio increases and the characteristic of advective velocity of vortex changes correspondingly. The advective velocity of vortex conspicuously increases with increase in the pressure ratio at axisymmetric mode.

Hiromasa Suzuki, Masaki Endo, Yoko Sakakibara

A Study on Screech Tone Emitted from Underexpanded Radial Jet

An underexpanded jet has typical shock-cell structure and strongly oscillates and its behavior is known to cause many industrial problems. An underexpanded jet radially issues from intake and exhaust valves of an internal combustion engine, a pressure control valve, and so on. When a supersonic jet exhausted from a circular nozzle impinges on a flat plate, the wall jet formed on the plate often becomes underexpanded and spreads out radially. Such underexpanded impinging jet is one of the models of supersonic jets on laser cutting process and glass tempering process. In this study, an underexpanded jet radially discharged from a circular slit nozzle, which consists of two circular tubes, is experimentally examined for different nozzle pressure ratios and for different diameters of tube. Jet structure is analyzed by means of visualization, e.g. Schlieren method. A noise emitted from the jet is measured and the frequency of screech tone is analyzed. The experimental results are compared with those of a two-dimensional jet issuing from a rectangular nozzle. As a result, in the radial underexpanded jet, multiple nodes of cell structure are visualized as ring-shaped shocks and collapse of the cellular structure of radial jet is found to occur at the upstream location in comparison with the case of rectangular jet. Furthermore, a comparison of visualized sound waves with the screech tone frequency reveals that the sound source of noise measured is in the vicinity of the end of the second cell and that the length of the second or third cell is one of the most important parameter of the frequency of the emitted screech tone.

Koichi Kawasaki, Hiromasa Suzuki, Masaki Endo, Yoko Sakakibara

Numerical Study on Flow Past a Cylinder with Different Inflow Parameters

The dynamic characteristics of the flow field behind a circular cylinder and its interaction with a wall boundary layer are investigated numerically. The 2D Navier–Stokes equations are solved using finite volume method with second-order accuracy for spatial and temporal schemes employing a laminar model. The flow is calculated for different Reynolds numbers at a particular gap ratio. The mechanism of how the shedding occurs and its dynamics, variation in Strouhal Number and trajectory of vortices are analyzed. The numerical results were validated against available experimental values in the literature. The variation of lift coefficient, switching and rippling frequencies for different inlet Reynolds numbers reveals the dependency of inflow parameters on wake dynamics.

Govind S. Syam, Gautam Rajeev, K. Muraleedharan Nair

Performance Evaluation of Unique Vortex Pump

It has been requesting to improve performances of high-pressure pumps which play a prominent role in building infrastructures such as power plants, seawater desalination plants, water and sewerage plants and so on. This paper prepares a unique vortex pump to get the higher head without an unstable performance. The forward blade makes the head coefficient increase while keeping the discharge and the maximum hydraulic efficiency. A guide vane installed on the casing wall is effective to get the higher head owing to strengthen the circulation of the vortex.

Toshiaki Kanemoto, Takahiro Otsubo, Morihito Inagaki, Ryo Hitachi, Mikio Kato

Numerical Analysis of Pulsating Flow in a Smooth Constriction Using Immersed Boundary Method

A major incentive for studying the flow of an incompressible fluid through a smooth constriction comes from the medical field. These constrictions represent arterial stenosis which is caused by deposition of intravascular plaques. To understand some of the major complications which can arise from arterial stenosis, the knowledge of the flow characteristics in the vicinity of constriction is essential. The main objective of the present work is to develop a two-dimensional computational model using a feedback forcing-based immersed boundary (IB) method to study steady and laminar pulsatile flow in a channel with a smooth constriction and investigate the effects of the Womersley number on the flow property. The study assumes the immersed boundary walls as rigid, and the flow is considered viscous, incompressible, and axisymmetric. The pulsatile flow simulations are done for a wide range of Womersley number within the physiological conditions for blood flow in arteries. The results obtained are in good agreement with the data from the literature.

Deepak Kumar Kolke, Arun M, Ranjith Maniyeri

Experimental and Numerical Investigation of Sloshing Phenomenon in Cylindrical and Rectangular Tanks Subjected to Linear Excitation

Sloshing is a complicated fluid movement. The problem of water sloshing in closed containers has been the subject of many studies over the past few decades. This phenomenon can be described as a free surface movement of the contained fluid due to sudden excitations. When frequency of external excitation is close to natural frequency of liquid in partly filled tank or amplitude of excitation is very large, sloshing motion in the tank will be severe. It becomes a resonant phenomenon of a violent fluid motion which predominantly occurs in partially filled tanks. Thus, the impact force to the side or ceiling of tank will be significantly strong; it may destroy the structure or cause instability to it. To study this sloshing phenomenon, this paper carried out an experimental and numerical procedure in partly filled rectangular and cylindrical tanks. Simulations are done in ANSYS with water and air as the fluids. Mesh has been generated in ICEM CFD. For the multiphase modeling, volume of fluid (VOF) model is used. A forced sinusoidal motion is provided as a profile to the tank. The simulation results are validated with the experimental results for the same tank configuration. The test rig enables manipulating a tank model so that slosh waves are represented. Slosh occurrence and its effects depend on several factors like environmental conditions, geometry of the containment structure, fill level, external forces due to acceleration/deceleration of the containment body, and hydro-structural interaction.

G. Unnikrishnan, Vaisakh S. Nair, S. Vishnu Prasad, Abhilash Suryan

Effects of Flap on the Reentry Aerodynamics of a Blunt Cone

Highly blunt configurations are generally used to decelerate spacecraft during reentry, but these configurations exhibit very poor aerodynamics characteristics, i.e., low lift-to-drag ratio. Attachment of flap may improve the aerodynamic characteristics of the blunt cone. Detailed analysis of the effect of ramp and flap over the blunt cone at supersonic speed has been done adopting numerical studies. Three-dimensional, steady, viscous flow through reentry capsule has been simulated using commercial CFD package FLUENTv15 and adopting k-ω (SST) turbulence model. Effect of flap angle on the base flow and the stability of the capsule have been studied at different altitudes using computational studies.

Senthil Kumar Raman, Kexin Wu, Heuy Dong Kim

Flow Characteristics of Confined G-CO2 and S-CO2 Jets

In this present work, a high-speed supercritical carbon dioxide jet emanates from chevron nozzle is computationally investigated. The primary objective of this work is to investigate the mixing nature of the jet with the chamber at supercritical and gaseous conditions at a different phase. This present study was performed using commercial computational fluid dynamics software Fluent V18.2. The mixing characteristics were analyzed with turbulent characteristics like turbulent kinetic energy and turbulent dissipation rate. It is found that flow characteristics of supercritical CO2 differ from the gaseous carbon dioxide. The results indicate that the chevron nozzle substantially increases the mixing characteristics of supercritical CO2. The influence of chamber diameter and length on the mass entrainment and jet mixing characteristics are also investigated.

Senthil Kumar Raman, Kexin Wu, Abhilash Suryan, Heuy Dong Kim

Numerical Analysis of Two-Liquid Flow in a Micro-Spiral Channel

Numerical analysis was performed to simulate two-liquid flows in a micro-spiral channel. Square, long vertical rectangle, long horizontal rectangle and circular cross sections were used to compose the spiral channels. The nominal hydraulic diameter of the channel is about 100 μm. The Reynolds number, pitch and mean diameter of the helical coil were varied to investigate their effect on the flow mixing. The mass conservation, alpha diffusivity and momentum conservation equations as the governing equations were used to mathematically model the problem, and the ‘twoLiquidMixingFoam’ solver within the OpenFOAM was used to solve the governing equations. As a result, it was found that the mixing of two liquids is greatly improved in the spiral channel in comparison with a straight channel. Pitch and mean diameter of the helical coil show a significant influence on the mixing performance.

M. M. A. Alam, Kazuya Watanuki, Manabu Takao

Fundamental Investigation to Predict Ice Crystal Icing in Jet Engine

Numerous supercooled droplets and/or ice crystals exist in a cloud. When an aircraft passes through a cloud, they impinge on the aircraft wing and fuselage, and also they enter into the jet engines. Such impinging droplets and ice crystals can form ice layers on the surfaces. This phenomenon is referred to “icing.” Apparently, the icing adversely affects the performance of an aircraft by reducing the lift and thrust, and it may cause a crash. To predict and understand the icing, a number of major research institutes and companies have been investigating the icing both experimentally and computationally. However, the icing is still one of major issues in the research and development processes of an aircraft and a jet engine because of the complicated interactions among various physical and weather conditions. In a jet engine, the main icing components are the fan blade, the fan exit guide vane (FEGV), the nose cone, the splitter, and the low-pressure compressor. Recently, the ice crystal icing in the high-pressure compressor attracts much attention because the ice crystal icing has been known as one of the major causes of engine power loss events in flight. The mechanism of the ice crystal icing is as follows: the ice crystals partially melt as they pass through the fan and the low-pressure compressor where the static temperature varies approximately from −30 to 100 (°C); the ice crystals impinge on the wall and create a water film on the warm surface of the components; the water film traps additional ice crystals, and the surface is cooled below the freezing point; the additional ice layer is build up on the surface. However, since the physics is so complicated, the ice crystal icing has not been predicted satisfactorily. In the present study, first, melting behavior of an ice crystal passing through a fan and a compressor of a jet engine was investigated. Since the ice crystal icing tends to occur in a high-bypass ratio jet engine, GE90 was selected as the target engine. In the simulations, thermal conduction, heat transfer, and evaporation were taken into account. The influences of ice crystal diameter and cruising altitude were focused to discuss the melting process of ice crystals under actual operational conditions. Second, using the computational results, we numerically investigated the possibility whether ice crystal icing actually occurs or not in the compressor. Icing on a two-dimensional compressor stator blade in a high-temperature environment was computed. Following conditions were assumed: the cruising altitude is 6000 (m), the material of blade is aluminum, and the diameter of an ice crystal is 100 (μm). We confirmed that the ice crystals that are half melt impact to the stator blade, cool it to the temperature lower than the freezing point, and form an ice layer on the leading edge.

Mikiko Iwago, Koji Fukudome, Hiroya Mamori, Naoya Fukushima, Makoto Yamamoto

Heat Transfer Enhancement of Concentric Double-Pipe Heat Exchanger Utilizing Helical Wire Turbulator

The present study involves fabrication and steady state experimental testing of double-pipe heat exchanger (DPHE) with turbulator. A helical wire has been inserted inside the inner tube of DPHE for creating extra turbulence to the flow through it. The effect of turbulator on heat transfer performance is studied. The working fluid used in the inner pipe and outer pipe is hot water and cold water, respectively. The test runs are performed at mass flow rates of hot and cold water ranging between 0.01 and 0.09 kg/s and between 0.01 and 0.04 kg/s, respectively. And the test is carried out in two separate modes, without using turbulator and with turbulator. Correlations and equations for flow properties and heat transfer characteristics were collected from various literature works involving flow through DPHE. The Nusselt number calculated from experiment values of the heat exchanger without turbulator is validated with the Dittus-Boelters equation for the pipe flow. A significant increase in the overall heat transfer coefficient is observed by using the turbulator in the inner pipe of the heat exchanger. Obviously, the increase in the performance comes with the cost of extra pressure drop. The reasons behind the enhancement of overall heat transfer coefficient and pressure drop of the DPHE using helical wire as turbulator were discussed. Dimensionless exergy analysis is carried out to study the changes by using the turbulator. In conclusion, for enhancing heat transfer performance, the helical wire turbulator can be employed in the heat exchanger.

K. V. Jithin, Arjunan Pradeep

Pseudo Shock Wave in a Slotted Duct of Constant Area

The flow inside a supersonic intake comprises a series of bifurcated compression waves and followed by an adverse pressure gradient region. This phenomenon referred to as pseudo shock wave (PSW). This complex flow feature mainly affects the performance and efficiency of the supersonic intake. The PSW mainly depends on various parameters like duct length and diameter, inlet and outlet conditions such as Mach number, pressure ratio, and boundary layer parameters. Understanding the flow features of PSW in a constant area duct is more important to develop a method to control to obtain optimum efficiency. There are several methods to control shock/boundary layer interaction like active or passive methods. In the present study, an attempt has been made to control pseudo shock wave using stream-wise slotted wall computationally. The Reynolds-averaged Navier–Stokes (RANS) simulation on controlled and uncontrolled pseudo shock wave has been carried out. The stream-wise slot can develop a counter rotating stream-wise vortices which energize the boundary layer and subsequently lead to smearing of shock foot and also preventing separation in the downstream region. The present simulations are carried out with a stream-wise slot in a constant area duct at different pressure ratio. The length of the pseudo shock wave is analyzed with and without slotted control.

Vignesh Ram Petha Sethuraman, Abhilash Suryan, Heuy Dong Kim

Characteristics of Shock Train Flow in Divergent Channels

In a Supersonic intake, the supersonic flow decelerates to subsonic speed inside the isolator by a series of compression waves. This wave phenomenon is referred to as shock train region. The length of the shock train is one of the main consent in designing the isolator. The isolator can be a constant or nearly constant area duct. The flow characteristic of shock train is depending on several parameters which makes the difficulties in designing the isolator for each particular engine. Also, the shock train strongly affects the performance of the various flow devices. The length of the shock train region can be able to predict using the upstream flow parameters; whereas, the diffusion region depends on both the upstream flow parameters and also influenced more by geometrical parameters. In the present work, the characteristic of shock train is analyzed using computational fluid dynamics method. The effects of upstream flow Mach number and different back pressure with the different divergent angle are considered in the present study. Studies have shown the total pressure loss increase with increase in divergent angle and also the blockage ratio decrease with the divergent angle.

Vignesh Ram Petha Sethuraman, Heuy Dong Kim

Numerical Investigation on Flow Separation Characteristics of Truncated Ideal Contour Nozzles

A numerical study is carried out to investigate the effect of truncation on flow phenomena such as separation and shock patterns using axisymmetric two-dimensional model of truncated ideal contour nozzle with different lengths. Three cases are considered with a nozzle of design Mach number 5.15 truncated to three different lengths. Flow characteristics are analyzed for nozzle pressure ratios (NPR) ranging from 10 to 60 and the results are compared for different lengths. The comparison shows that, at low NPRs, when the separation position is near the throat area, separation is unaffected by the truncation. As the separation positions move toward the nozzle exit, an increase in NPR results only in compression of the separation zone. The variations in flow structure and shock patterns are analyzed for a varying range of pressure ratios for all nozzle length which can be co-related to side-loads. The results of numerical study confirm previous experimental results.

Kiran Kumar, Abhilash Suryan, V. Lijo, Heuy Dong Kim

Flow Rate and Axial Gap Studies on a One-and-a-Half-Stage Axial Flow Turbine

Flow in a turbine stage is complex, and improving performance is a major challenge. Hence, it is still the topic of concern in the gas turbine community. Flow rate and axial gaps are of the few important parameters that affect the performance of a turbine. Present work involves the computational study of a one-half stage axial flow turbine with axial gaps of 15 and 50% of the average of the rotor and stator axial chords. For each axial gap, analysis is done at three flow coefficients, namely 0.68, 0.78 and 0.96. The turbine components nozzle, rotor and stator are modeled for both the axial gaps. Each axial gap requires distinct modeling and grid generation of fluid domain consisting of all the components. Mid-span pressure distribution of the stator for the design configuration is compared with the experimental results and found to be in good agreement. Pressure, entropy, Mach number and TKE distributions along with torque and efficiency are analyzed for both the configurations. From inlet to outlet of the stage, variations of parameters are plotted in contours and x–y plots. Flow is visualized clearly in mid-chord contours, and mass average values are considered at each position. Flow impingement, presence of wakes, stagnation and saddle points are observed. Entropy drop across the stage is higher for 50% gap. Rotor torque and efficiency decreased with increased axial gap. Trends are changing with flow rate. Results thus specify that the turbine performance is reliant on flow rate and axial gap.

Rayapati Subbarao

Condition Monitoring of Cavitation-Induced Centrifugal Pump

Cavitation-induced defects in a centrifugal pump are severe causing reduced efficiency, head loss, low discharge, and ultimately premature failure of the system if it goes undetected. This necessitates the need for its condition monitoring for the detection of early indication of cavitation. Conventional condition monitoring techniques like vibration and acoustics spectrum analyses can be used to detect the presence of mechanical abnormalities present in the system. In this paper, a centrifugal pump is monitored in normal running and cavitation-induced condition with the aid of vibration and acoustics analyses. Observations are made at different rotational speeds and at various pressure levels. FFT analysis is carried out to trace discrete frequency components in low-frequency range up to 800 Hz and at high-frequency range from 3.3 to 4.4 kHz. Variation in amplitude of discrete frequency component, its sidebands, and its harmonics is an indication of cavitation. Results showed a significant increase in amplitude in high-frequency region during cavitation-induced condition, whereas in low-frequency region amplitude levels decreased.

Krishnachandran, A. Samson, Akash Rajan

Comparison of Flow Features Near the Wake of Circular and Elliptical Cylinders for Different Gap to Diameter Ratios

The fluid in motion exerts force on the solid body immersed in it such as flow around an airplane, automobiles and underwater pipelines. The flow around a cylinder near a flat plate boundary layer can be related to an upward force on the aircraft during landing. This ground effect phenomenon is often characterized by an increase of lift accompanied by drag force reduction. It depends on the flow velocity, surface body roughness, body orientation immersed in the fluid with the direction of fluid flow and the object configuration. A numerical investigation is carried out using ANSYS Fluent. Two-dimensional unsteady Navier–Stokes equations are solved using finite-volume method with second-order accuracy for spatial and fourth order for temporal schemes. A detailed grid-independent test is carried out and the numerical results were validated against available experimental values in the literature. The present study illustrates the flow field evolved and the wake-boundary layer interaction when flow past a circular and elliptical cylinder at Reynolds number (ReD) 40 and 1000, where D denotes the diameter. The interaction of shed vortex developed with the flat plate boundary layer is predominant for a circular shaped cylinder when compared to an elliptical one. This event becomes less prevalent as the gap to diameter ratio increases. The results demonstrate shear layer formation, its shedding, its interaction with the boundary layer, etc.… The varying non-dimensional frequency, lift and drag coefficient along with the iso-contours of vorticity show the influence of gap ratio on the modification of wake dynamics and evolution of the wall boundary layer. For low gap ratio, it appears that the wake-boundary layer interaction becomes less prevalent as the shape changes from circular to elliptical. It is observed that for a higher gap to diameter ratio, this interaction becomes less prevalent for both circular and elliptical cylinders.

K. Muraleedharan Nair, S. Vishnu Prasad, Vaisakh S. Nair

Characteristics of the Supersonic Flows Over 3-D Bump

In supersonic flows, bumps were used for the injection of fuel into the flow field due to its high mixing efficiencies without much change in the upstream conditions. Research on wave drag reduction using contour bumps in transonic aircraft wings has been an active research topic in the aerospace sector in recent years. It was estimated that about 5–15% of wave drag reduction could be achieved in a transonic aircraft with rounded contour bumps installed on to its wing surfaces. Although there are many types of research in this field, the underlying flow physics of rounded contour bumps is less well understood. Although using contour bumps could provide desire performance in drag reduction and high total pressure recovery in transonic and supersonic aircraft, it is known that adverse effects can be induced by flow separation and spanwise vortices formation appear downstream of the bump crest of the bumps. As a result, it is important to investigate the flow separation characteristics of contour bumps to have a better understanding of the physics of bump flow. The present study aims to simulate the flow conditions computationally using the finite volume solver. The flow structure and the spanwise flow patterns are analyzed for a better understanding of the flow physics when we introduce the injection to the flow field. The results show that injection effectiveness can be increased with increasing jet total pressure ratio.

Jintu K. James, Heuy Dong Kim

Effects of the Asymmetrical Vortex Interactions by a Variable Swept Vortex Generator (VSVG) on Heat Transfer Enhancement

Unsteady RANS simulation of high-speed flow and heat transfer over a heated plate with a variable swept vortex generator (VSVG) is presented. Unsteady three-dimensional turbulent compressible flow and heat transfer are numerically solved using Advection upstream splitting method (AUSM)-based Finite Volume Solver. The computational procedure has been validated using the experimental data reported for a similar kind of vortex generator placed over a heated plate. Simulations have been performed for vortex generators with the same lateral sweep on both sides as well as different lateral sweep on either side. Variable swept vortex generator sets in an asymmetrical vortex–boundary layer interaction which can enhance the heat transfer in comparison with symmetrical vortex interactions realized by a similar vortex generator with the same lateral sweep. It is observed that the asymmetric counter-rotating vortex pair is generated when the high-speed flow spills over the slanting surface of the vortex generator, which can enhance mixing and transport downstream.

G. P. Aravind, M. Deepu

Estimation of Shear-Induced Blood Damage in Artificial Heart Valve Components

Shear-induced blood damage is a prominent failure mode in cardiovascular devices. This failure mode results from structural and/or functional damage of formed elements of blood like red blood cells, platelets, white blood cells, etc., due to exposure in an environment where shear stresses are relatively high. Simplified models are required to allow computations to be employed in flow analysis of mechanical heart valve. Common simplifications include two-dimensional approximations, steady flow approximations, simplifications of configuration, or assuming fixed rather than moving occluder in valves. Studies have shown that shear stresses in excess of 17.5 Pa can result in the initiation of shear-induced cell damage. So, it is important for medical device designers to ensure that extremely high shear stresses are not occurring on the device surfaces in the design of an optimal heart valve from point of view of hemodynamics. TTK Chitra heart valve, Model TC2 is a mechanical heart valve being developed jointly by TTK Healthcare Limited and Sree Chitra Tirunal Institute for Medical Sciences and Technology (SCTIMST). This study attempts to develop a model for estimating shear stress levels during different steady flow rates corresponding to varying velocity profiles of a typical cardiac cycle on mitral valve components. A computational model was employed to study the distribution of velocity profiles and shear stress distributions in and around structural elements of the TTK Chitra heart valve. The shear stress estimates on the surface of the valve components were obtained for varying cardiac output conditions. Results indicate that the turbulent shear stresses in excess of 17.5 Pa, acceptance range for hemolysis behavior, was observed only in less than 5% area of the components. Most of these zones where turbulence stresses are high are in corners and edges where the resident time of blood cells are extremely low, of the order of few milliseconds.

Padman R. Bijoy, C. V. Muraleedharan, Prasanth P. Nair, Abhilash Suryan

Dynamic Thermal Modeling and Simulation of Boiling Heat Transfer in PCM-Assisted Diverging Microchannels

Micro-miniaturization has open up new challenges in negotiating high heat flux in electronics cooling applications. A heat sink design using a diverging fluid passage surrounded by latent heat storage is analyzed. A dynamic thermal model based on energy balance among multiple heat-transfer modes is developed. Solution of this model is used to analyze the thermal behavior when the system is subjected to rapid changes in load or operating parameters. Results of the simulations indicates that the PCM storages in diverging channels help to protract the boiling heat-transfer conditions compared to the straight microchannel. Present configuration offers passive control of rapid temperature development in coolant and chip surface.

B. Indulakshmi, G. Madhu

Blade-to-Blade Flow Distribution in a Counter-Rotating Turbine with Flow Rate

It is projected that just 1% improvement in the efficiency of gas turbine would save millions of dollars depending on the application and usage. Thus, it has been the prime interest of the researchers to investigate their performance by analysing the nature of the complex flow in a turbine. In counter-rotating turbine (CRT), nozzle is followed by two rotors that rotate in the reverse direction of each other. Flow interaction between the stationary nozzle and rotor 1 as well as rotor 1 and rotor 2 further adds to the complexity of the flow. None of the earlier works could clearly describe the flow pattern through CRT stage. In this context, present work finds significance with the modelling and simulation of CRT blade rows with respect to the identification of blade-to-blade flow for various flow rates. Equivalent mass flow rates of 0.091–0.137 are considered. Flow rate has significant effect on the pattern of the flow. In rotor 1, the loss region is less compared to rotor 2 for all the flow rates suggesting better performance. Loss regions get initiated at the exit of the nozzle that get expanded from the mid-chord section of the rotor 1 on the suction side. These losses further get propagated till the exit of the turbine stage. The transmission of losses from the mid-chord region of rotor 1 to rotor 2 is more due to rotational effects. As the flow rate is increased, more flow and turbulence losses in rotors are observed with varied magnitude.

Rayapati Subbarao, M. Govardhan

CFD Simulation of Multiphase Droplet Evaporation

Modeling droplet evaporation is of paramount interest in applications such as spray cooling and scramjet combustion. This study presents the results of CFD simulation of water evaporation phenomenon in a rectangular duct using Fluent (ANSYS, Inc.). The spray consists of uniformly sized spherical droplets of 0.1 mm diameter injected into the incoming air stream with a predefined velocity profile. Reynolds-averaged Navier–Stokes equations are solved with k-ε turbulence model. The mass, momentum and heat transfer between droplets and air are solved using the inbuilt discrete phase model (DPM) of Fluent (ANSYS, Inc.). The DPM is based upon Lagrangian treatment for particles and Eulerian treatment for the continuous phase. The results obtained are compared with that of the literature wherein a similar case was solved numerically using Eulerian–Eulerian treatment for both discrete and continuous phases. The particle diameter and temperature at the outlet wall are compared with the literature, and the difference is found to be less than 2%. Limitations and further scope of this study are discussed.

Mayank Kumar, Shubham Maurya, Vinod Kumar

Steady-State and Transient Simulations of Heat Dissipation from an Electronic Component Kept in a Closed Enclosure Using OpenFOAM

All electronic components and circuitry generate heat when current is passed through them due to its resistance. Reliable open-source solvers for obtaining the heat dissipation rate are of great importance to the industrial sector. The failure rate of the electronic components can increase exponentially with temperature. Without proper design and control, high rate of heat generation results in high operating temperature of electronic equipment, which reduces their safety and reliability. Therefore, before manufacturing of equipment, proper study in the heat generation should be conducted, and the type of cooling system shall be selected appropriately. This work studies the heat dissipation of built-up heat in electronic components. The open-source CFD package OpenFOAM is used to develop a numerical model of an electronic component placed in a closed enclosure. An experimental apparatus is used to validate the results obtained from CFD analysis. The validated CFD model can then be used to simulate heat dissipation from any component within the range of velocities for which the test is conducted.

Bobin Saji George, Markose Paul Aajan

Optimum Design of a Plane Diffuser Using Finite Element Method, Surrogate Model and Genetic Algorithm

An optimum design of a plane diffuser is determined in this work to maximize the pressure rise. The diffuser consists of a diverging section followed by a straight section in the downstream. The design variables are angle of diffuser (α), diffuser length (L1) and length of straight section (L2). The mathematical model is the set of partial differential equations of incompressible flow in Cartesian coordinate system. Numerical solution is obtained using Freefem++, an open-source FEM compiler. The methodology starts with a sensitivity analysis for determining the range of design variables in which the pressure recovery has a significant dependence. Next, a sampling plan with 100 data points having maximum spacial spread is taken by using Latin Hypercube experimental design. The numerical solution is obtained for 100 sample data points and then computed the pressure recovery for each design. The final optimization is carried out using genetic algorithm which requires pressure rise data corresponding to a large number of design variables sets. In order to meet this requirement of dependent variable, a surrogate model is developed using simple Kriging. This is basically a multi-variable regression model for pressure rise as a function of the design variables.

Aji M. Abraham, S. Anil Lal, P. Balachandran

Shock Tube Performance Studies with Different Driver and Driven Gases Using Numerical Simulation

This paper evaluates the performance of the shock tube with air and helium as working fluids in the driver and driven sections, respectively, using numerical simulations. For this, a 2D planar geometry of shock tube is made. Navier–Stokes equation reduced to Euler equation is solved with the inviscid model. The dependency of shock Mach number, temperature and pressure behind the incident and reflected shock on diaphragm pressure ratio are obtained. The values of Mach number, temperature and pressure obtained for various diaphragm pressure ratios of air–helium shock tube are compared with that of shock tube with air in both driver and driven sections. Numerical simulations were carried out using CFD solver ANSYS Fluent. At lower diaphragm pressure ratios, there are no significant changes in Mach number generated. But when pressure ratio increases, there is considerable change in shock Mach number which is observed. The helium–air combination is able to produce higher Mach numbers compared to air alone. The obtained results are validated analytically for the air–air combination. 25% higher shock Mach number, 24% higher temperature behind the incident and 26.7% higher temperature behind reflected shock are obtained for helium–air model when compared to air–air model.

J. P. Ananthu, N. Asok Kumar

Flame Characteristics and Pollutant Emissions of a Non-premixed Swirl Burner with Annular Swirling Fuel Injection

Flame stabilization under highly turbulent conditions is commonly achieved using swirling flows in gas turbine applications. The present study investigates the influence of swirling fuel injection on the flame stabilization and emission characteristics of non-premixed and swirl stabilized model gas turbine burner. For the comparative study, three different fuel injection configurations with respect to the swirling airflow (in counterclockwise direction) are chosen—(a) fuel flow unswirled, (b) fuel swirl in clockwise direction, and (c) fuel swirl in counterclockwise direction. The burner is operated with methane fuel and air, for different air nozzle Reynolds numbers 1310, 1970, and 2620 based on the hydraulic mean diameter. The mass flow rate of fuel is varied to get a global equivalence ratio variation from 0.2 to 1.0. In order to compare the structure and flame stabilization location, flame luminosity measurements are carried out. OH* chemiluminescence images are used to estimate the size and shape of heat release zone along with pollutant emission measurements for each case. It is observed that the burner has very low NOx emission at all investigated operating conditions. NOx emission increases with increasing global equivalence ratio. In comparison, case ‘b’ shows very low NOx emission with respect to the cases ‘a’ and ‘c’ for all investigated airflow conditions. Flue gas temperature for case ‘b’ also has lower values when compared to others. From the flame luminosity and OH* chemiluminescence studies, it is seen that the global equivalence ratio plays an important role in the location of flame stabilization. OH* intensity varies with respect to equivalence ratio for all cases. For case ‘a’, OH* radical distribution is more spread out and more uniform whereas the others have a localized heat release zone closer to the inner shear layer. Also, the flame standoff distances for the case ‘c’ are less compared to cases ‘a’ and ‘b’. This indicates fast mixing and high reactivity of fuel–air mixing. In general, for a fixed global equivalence ratio and fuel injection configuration, the change in Re did not have any influence on the flame stabilization location. This demonstrates the high stability of the flames produced in this burner.

R. S. Prakash, K. S. Santhosh, Rajesh Sadanandan

Experimental and Numerical Investigation of Natural Convection Within Vertical Annulus

Natural convection flow in a vertical annulus with an isothermally heated bottom and a uniformly cooled top surface is experimentally investigated using laser visualization technique. The outer and inner walls of the annulus are adiabatic. The annulus is heated from the bottom, thereby causing upward movement of air which is then cooled by the top wall. This heat transfer process leads to the formation of natural convection loops in the annulus. These convection loops were visualized using laser visualization techniques. Three dimensional, unsteady and a highly unstable flow was observed for a Rayleigh number 2.86 × 106 within the annulus having height 650 mm, aspect ratio 10 and annular gap 70 mm. To validate the experimental results, an in-house numerical code was developed in FORTRAN. The numerical results also show the existence of three dimensional, unsteady and chaotic flows in the annulus. A correlation for the average Nusselt number for varying heat inputs to the bottom plate and closed top plate was developed using SPSS 16 software. The Nusselt number obtained from the correlation was plotted against experimental values and showed an almost linear variation within specified error limits.

V. Vinod, S. Anil Lal

Aerothermal Qualification of Melamine Foam-Based Thermal Pads for Tankages of Liquid Engine of a Typical Launch Vehicle

Propellants of a liquid engine of a launch vehicle are filled into tankages at low temperatures and should be maintained below a specific temperature until liftoff from ambient heating. Low absorptive Melamine foam based thermal pads developed by VSSC to be inducted as TPS on liquid propellant tanks. Though the purpose of such an insulation scheme is fulfilled just before the liftoff, but to ensure the integrity of the system, it has to be qualified for flight environments. Aerothermal qualification tests which include ground-level thermal simulation, high altitude thermal simulation, simulation of aeroshear loads and flammability tests are carried out for qualifying the integral insulation scheme post liftoff aerothermal environments, before inducting in flight. Test specimens are subjected to heat flux history corresponding to levels experienced on the surface of the tankages during launch for ground-level thermal simulation tests, in high altitude thermal simulation (HATS) tests, thermal simulation is carried out in vacuum, and for aeroshear testing, specimen subjected to shear loads by blowing compressed air at predetermined levels to ensure that entire specimen surface experiences shear levels greater than or equal to the maximum shear levels observed during the flight. Flammability qualification tests are required to ensure the insulation system do not catch fire in-case any exhaust gases are impinged. Tests are carried out by exposing the specimen to an oxy-acetylene flame to simulate required heat load. This particular work reports the multiple aerothermal tests carried out on smaller specimens of the insulation scheme as part of qualification.

N. Uday Bhaskar, K. Vanitha, P. B. Chiranjeevi, G. Kumaravel, S. Jeyarajan, B. Sundar

Aerodynamic Configuration Analysis of a Typical Inflatable Aerodynamic Decelerator

A fore-body attached inflatable ballutes were considered for the aerodynamic analysis. Detailed CFD studies for sensitivity of aerodynamic coefficients to cone angle, varying payload length and center of gravity location were carried out. Flow simulations carried out for multiple angles of attack (AoA) at different altitude conditions. Variation of aerodynamic coefficients, i.e., axial force coefficient, normal force coefficient and pitching moment coefficient with angle of attack at multiple altitudes and free stream conditions is reported. Analysis for tumbling cases was carried out at higher altitudes. Aerodynamically, an IAD configuration, which is more stable and with maximum drag, i.e., with minimum ballistic coefficient is considered ideal. Based on the parametric studies, an optimum configuration was arrived, which was statically stable with (dCm/dα) at 0° of −0.18 and a ballistic coefficient of 4.6 which meets the mission requirements. Variation of pitching moment coefficient about stagnation point with angle of attack clearly indicates that IAD configuration is statically stable to 60° AoA.

N. Uday Bhaskar, B. Deependran, V. Ashok

Numerical Simulation of Blade Vortex Interaction (BVI) In Helicopter Using Large Eddy Simulation (LES) Method

In this paper, computational fluid dynamics (CFD) viscous flow simulation of BO-105 isolated helicopter rotor blades was simulated using commercially available STAR-CCM + software. The aim of these simulations is to capture the complex flow dynamics and blade vortex interaction (BVI) noise generation in hover configuration. In order to capture the complex nature of BVI and viscous wake precisely and accurately, large eddy simulation (LES) method was used. Overset mesh was used as mesh technique. The mesh technique and number of cells play an important role in capturing this complex phenomenon. Computational aero-acoustics (CAA) method was used to capture the noise generated due to the rotation of rotor blades. Ffowcs-Williams–Hawkings unsteady equation formulation was used to capture the far-field acoustics. Both CFD and CAA together helped to obtain the flow dynamics as well as far-field noise generated. The hover performance parameters obtained from numerical simulation showed good agreement with the theoretical and experimental data. The frequency spectral analysis of the acoustical data showed number of peaks that correspond to blade passage frequency (BPF) and its harmonics. The sound pressure level SPL of receivers at $$ \sqrt 2 \text{m} $$ in Cartesian coordinates at 45° elevation in 1st and 4th quadrants was greater compared to that of rotor plane receivers. The maximum SPL of 121 dB was measured by receiver directly below the rotor hub of the helicopter.

John Sherjy Syriac, Narayanan Vinod

Noise Reduction in Subsonic Jets Using Chevron Nozzles

The exhaust of the jet engines used in commercial (subsonic) aircrafts produce a lot of noise known as jet noise. This noise has adverse effects on the population living nearby the airports. However, the noise levels are above the permissible limit and thus need more attention. This paper reviews some of the techniques for noise reduction and mainly focuses on the use of chevron nozzle in reducing the jet noise. Large eddy simulations are performed for a simple nozzle and chevron nozzle with triangular wedges at the rear circumference of the nozzle with same boundary conditions. Acoustic data is collected at different receiver locations to understand the effect of chevrons in jet noise reduction. The result of the simulations shows that chevrons are good attenuators of jet noise.

Suyash Kumar Gupta, Narayanan Vinod

Signature of Linear Instability in Transition Zone Measurements in Boundary Layer

The hydrodynamic stability and transition in the boundary layer over a flat plate is a largely discussed topic and various researches have been done on the same with fairly accurate results. This is an important area of research because it can be used to approximate boundary layer over streamlined objects with very large radius of curvature, like airfoils. For such approximations, the development of boundary layer in favorable as well as adverse pressure gradients has to be thoroughly studied. Transition to turbulence is a result of growth of instabilities in the transition region. Hydrodynamic stability of laminar boundary layer when developed in the mathematical framework gives us insight into the wavenumber and frequency of unstable modes, which are responsible for transition. Because of its stochastic nature, it is impossible to develop a mathematical theory for transition zone, and therefore, we rely on experimental measurements and numerical simulations. In this work, we studied the relation between laminar instability and transition measurements. We then studied zero and adverse pressure gradient boundary layers to establish the connection. Orr–Sommerfeld equation deals with instability in parallel flows when the instabilities are in its linear stage. This equation is solved using Chebychev collocation method to determine the most unstable modes. We measured the transient wall pressure in the transition zone to establish a direct relation with laminar instability wave characteristics. Primary results indicate that the relation is prominent in adverse pressure gradient boundary layers, while it is obscured in Blassius boundary layers.

Akash Unnikrishnan, Narayanan Vinod

Numerical Simulation of Underwater Propulsion Using Compressible Multifluid Formulation

Underwater propulsion has various applications and is of great interest. Pressurized gaseous jet flows through a nozzle into water at various depths. The flow structure and processes are unsteady and involve multiple phases. There are various phenomena taking place when gaseous jet is injected into water, namely expansion, bulging, necking/breaking and back attack. Wave travel and information travel in gas and water medium are significantly different. Hence, compressible multifluid formulation which takes into account that all the information travel through the stiffened gas equation of state is used for numerical simulation. Finite volume method is used for spatial discretization and explicit four-stage Runge–Kutta scheme for time integration. For validation of the code developed, air–water shock tube case is carried out. As an application, an integrated unsteady simulation of nozzle and plume flow field of a convergent-divergent nozzle at sea level underwater is simulated. Unsteady flow features and their effect on thrust are computed. Nozzle wall pressure is integrated at various instances to get the thrust and the unsteady thrust has been related to flow features.

Annie Rose Elizabeth, T. Jayachandran

Effect of Diglyme on Simultaneous Reduction of NO and Smoke in a Third-Generation Biofuel Derived from Waste in a Tractor Engine

The present work aims to achieve simultaneous reduction of NO and smoke emission using waste tire pyrolysis oil (TPO) a third-generation fuel along with cetane improver namely diglyme (DGE) in a twin cylinder CI engine used in tractors. The solid waste tire disposal is getting much attention due to the environmental and health effects to humans. One of the methods to recycle used tire is to convert it to useful fuel to replace diesel in CI engine. Fuel derived from waste tire has comparable calorific value compared to diesel. TPO possess high viscosity and low cetane index causing improper atomization and increased ignition delay. This property of TPO reduces brake thermal efficiency (BTE) with higher NO and soot emissions. BTE for TPO is reduced by blending cetane improver, namely diglyme which subsequently improves the BTE along with reducing NO and smoke. The tests were conducted at constant speed of 1500 rpm with constant fuel injection pressure and timing. The tests were conducted at various load conditions corresponding to 25, 50, 75 and 100% of maximum brake power (BP). DGE was blended 10 and 20% with TPO on volume basis. NO emission increases from 1413 ppm for diesel to 1565 ppm for TPO and reduces to 1350 and 1235 ppm for TPO + DGE10 and TPO + DGE20 at 100% load. Smoke opacity increases from 62% for diesel to 70% for TPO and reduces to 67 and 63% for TPO + DGE10 and TPO + DGE20. TPO + DGE20 reduces maximum NO and smoke emission but brake thermal efficiency (BTE) is less due to high latent heat of vaporization. Hence, TPO + DGE10 is identified as optimum blend to simultaneously reduce NO and smoke emission with improved performance.

V. Edwin Geo, S. Madhankumar, S. Thiyagarajan, D. Boopathi

Assessment of Aerodynamic Characteristics on Shock Vector Control

Nowadays, fluidic thrust vector control technique is one of the key strategies for redirecting various air vehicles such as aircraft, guided missiles, and small modern rockets. Fluidic thrust vector control method mainly includes shock vector control, co-flow and counterflow vector control, throat-shifting vector control, and dual-throat nozzle vector control. Especially, shock vector control is a simpler and more convenient technique that the supply system of secondary flow is established in the supersonic portion of a conventional convergent–divergent nozzle. Then, the primary flow deflection can be realized through an induced oblique shock. In the present work, three-dimensional computational fluid dynamics methods were performed with different affecting factors. For the validation of numerical methodology, the CFD results were compared with experimental data obtained at the NASA Langley Research Center. The pressure distributions along the upper and lower nozzle surfaces in the symmetrical plane were excellently matched with experimental results. Theoretical analysis of several performance parameters was conducted, and numerical simulations were carried out to study the variation of SVC performance. Computational results were based on well-assessed SST k-ω turbulence model. Second-order accuracy was selected to reveal more details of the flow-field as much as possible. Two affecting factors were studied, including the slot width and the working gas (air, argon, carbon dioxide, and helium). Performance variations were illustrated, and some constructive conclusions were gained to provide the reference for further investigations in the SVC field.

Kexin Wu, Abhilash Suryan, Heuy Dong Kim

Effect of Train Speed on the Formation Process of Entry Compression Waves Generated by a High-Speed Train Entering Tunnel

An entry compression wave is the first of the successive waves produced as a high-speed train enters a tunnel. The compression wave generated by the train head continues to develop first and thereafter travels at the local speed of sound propagating inside the tunnel. These waves create a multitude of complicated wave phenomena causing distinct aero-acoustic problems, which have long been the concern of researchers. The pressure intensity and the amplitude of this particular wave vary according to the train speed and tunnel characteristics. Hence, to understand the effect of train speed on the formation process of the compression wave, a computational investigation using commercial computational fluid dynamics (CFD) solver FLUENT 17.1 has been performed. The train at a given speed is moved as a rigid body, and the stationary mesh is updated using the dynamic meshing update techniques. The numerical scheme for this specific problem has been validated against a reduced scale experimental setup. Further, five different train speeds have been studied for an axisymmetric train entering a uniform cross-sectional tunnel. The pressure inside the tunnel is monitored throughout the wall to study the development process of the compression waves, and the results are comprehended with pressure plots and contours.

Rohit Sankaran Iyer, Dong Hyeon Kim, Tae Ho Kim, Heuy Dong Kim

Comparison of Working Fluid Models Used in the Analysis of Main Steam Line Break Accidents of Steam Generators in Nuclear Power Plants

The main steam line break (MSLB) in a steam generator is one of the most critical accidents that can occur in a nuclear power plant. When such accidents happen, the steam generator is exposed to high pressure (7.8–0.101 MPa) and temperature differences (273–15 °C) in a short time. In such a case, the selection of the working fluid model is a very important parameter in the numerical analysis because of the steam property changes abruptly. When analyzing compressible fluids, using ideal gas model is one of the simplest ways for calculating the change of the fluid property value (density) according to state variable (temperature and pressure). However, this model becomes more inaccurate at higher pressures and lower temperatures. Therefore, a number of more accurate real gas models have been developed as like IAPWS, Redlich-Kwong, and Peng-Robinson models. In this study, we want to identify the differences in the ideal gas model and real gas models that can be used to carry out the main steam line break accident analysis. In this study, CFD analysis of the main steam line break (MSLB) was performed using the ideal gas equation model and the real gas model, which can be used as the working fluid model. The results show that the real gas models—IAPWS, Redlich-Kwong, and Peng-Robinson are more reliable than the ideal gas model.

Junho Jeon, Yoonhwan Choi, Yeonwon Lee
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