Proceedings of Fluid Mechanics and Fluid Power (FMFP) 2023, Vol. 1

In the present work, we study the vortex-induced vibrations of an elastically mounted cylinder with a flexible splitter plate in its wake. Two splitter plate flexural rigidities have been investigated with splitter plate length of 2D (D is the diameter), one where the plate is completely rigid (EI/ $$b \xrightarrow \infty $$ b → ∞ ), while in the other case, the plate is flexible with flexural rigidity (per unit width), EI/ $$b=5.5\times 10^{-6}$$ b = 5.5 × 10 - 6 Nm. The experiments are done in a water tunnel at low mass and damping values of $$m^*$$ m ∗ = 5.98 and $$\zeta $$ ζ = 0.0038 over a range of reduced velocities from $$U^*$$ U ∗ = 4 to 10. Cylinder response, flexible splitter plate deformations, and forces on the cylinder have been measured, for both the splitter plate cases, and a reference case of a bare cylinder. The differences in cylinder response and forces on the cylinder between the cases are highlighted, and a more systematic study of splitter plate flexural rigidity on the cylinder response is presently being undertaken.

Shock waves are a well-known phenomenon observed in compressible flows. Practically every flow is compressible, and hence, the occurrence of shock waves is very common. Shock waves have a wide range of applications. Oil extraction, drug delivery, metal forming, and medical surgeries are few of them. In this study, the phenomenon of shock wave interaction with water has been investigated experimentally. This is relatively a naive subject since it involves the interaction between a compressible medium and a relatively incompressible medium. There are many methods to generate a shock wave out of which shock tube is the most common one. Shock tube is a common device used by researchers to generate a shock wave. For the interaction to happen with water, the shock wave must be focused on it, for which a pipe bend has been used as an extension of the shock tube. A rectangular water tank has been used to hold the water. The experiments have been performed to determine the effect of the shock wave, Mach number, and the distance between the pipe bend’s opening and the water surface, on the shock–water interaction.

The scope of this study is to examine the effect of chevrons on the flow and acoustic properties of the supersonic free jet by comparing CD nozzles of three different configurations: baseline, 6-chevrons, and 12-chevrons. Experiments were conducted for various NPRs ranging from 2.25 to 4.25, using the blow-down supersonic wind tunnel. The flow visualization was done with a Schlieren setup and the acoustic signature was captured using a sound level meter at various observation points from the jet. Visualization images indicate that the chevrons alter the free-jet structure of the supersonic flow by reducing the shock cell length and adding streamwise vortices to the flow. Acoustic analysis reveals that both chevron nozzle configurations accomplish significant noise mitigation compared to the baseline nozzle; the 12-chevron configuration mitigates noise better at NPR 2.25, while the 6-chevron configuration shows superior performance at NPR 2.75 and 3.25.

Diatomic and polyatomic molecules are characterized with additional degrees of freedom that may not be in equilibrium with each other in non-equilibrium flows. The assumption of common temperature for all modes may not be justified as the degree of non-equilibrium increases. In this study, we consider multi-temperature approach with NSF formulation to model rotational non-equilibrium in shock structures at high Mach number flows in diatomic gases. Parker’s model for rotational relaxation has been employed to model energy exchange between translational and rotational modes. Vibrational energy has not been considered for simplicity. Common gases such as $${\text {N}}_2$$ N 2 , $${\text {O}}_2$$ O 2 , and $${\text {Cl}}_2$$ Cl 2 have been chosen to study the effect of gas properties on relaxation phenomena. It has been found that shock structures in $${\text {N}}_2$$ N 2 and $${\text {O}}_2$$ O 2 are similar while that in $${\text {Cl}}_2$$ Cl 2 differs considerably. Besides, the effect of variable and constant rotational collisional numbers, viscosity models, and Mach numbers have also been carried out. Simplified models for viscosity variation with temperature such as power law model have been used to make the study simple but intuitive.

The study presents an experimental investigation of flow field, an elevated circular jet of aspect ratio of 9.0, exiting orthogonal to crossflow. The experiments are conducted in a recirculating low-speed water tunnel. Both flow visualization and time-averaged particle image velocimetry (PIV) measurements are conducted to capture the flow dynamics. The PIV technique is used for the measurement of mean velocities and turbulent kinetic energy in both the symmetric (XY) and wall-parallel (XZ) planes. The aim of the study is to analyze the jet and its wake at a velocity ratio (R) of 3.0 and Reynolds number (Re) of 1000. The jet shear layer exhibits anti-clockwise vortices on the windward side and clockwise vortices on the lee-side of the jet. Streamline plots reveal the presence of an unstable focus in the jet-wake region in the symmetric plane. A detailed sectional analysis at different XZ planes indicates the existence of two sets of vortex pairs in the mean spanwise velocity contour, located both upstream and downstream of the jet. These pairs suggest the separation of crossflow around the jet on the upstream side, while the shear layer enters the jet-wake region on the downstream side. The study finds that the turbulent kinetic energy and Reynolds shear stress are highest on the uppermost plane at y = 2.5, which is situated far from the free-end of the stack.

Cardiovascular diseases are major contributors to mortality, with valvular disease being a primary precursor. A valve failure is common and can lead to a decline in pumping function, potentially resulting in cardiac arrest. Conducting in-vivo experiments on human heart valves, whether native or artificial, poses significant challenges. However, computational fluid dynamics (CFD) combined with fluid structure interaction (FSI) provides an effective and cost-efficient means of investigating the haemodynamics of both natural and artificial heart valves. This approach offers valuable insights for diagnostic and clinical applications. In this study, we developed a haemodynamic model of the mechanical heart valve using smoothed particle hydrodynamics (SPH). The model was successfully validated against traditional finite volume methods (FVM) and experimental data. We demonstrated that SPH is well-suited for simulating heart valve function due to its Lagrangian description of motion, which is particularly advantageous for FSI. Furthermore, to enhance the clinical relevance of the model, we have conducted three case studies of the mechanical valve malfunction due to leaflet restriction resulted by pannus and thrombus formation. The proposed SPH/FSI technique presented here provides a unique and valuable tool for accurately modelling the transient haemodynamic behaviour of the malfunctioned bi-leaflet heart valve under different velocity phases.

The main objective of this study is to explore the flow structure and its acoustic radiation from a military-style supersonic nozzle with and without chevrons of Md 1.4. Schlieren images were captured for both baseline and chevron nozzles, and these images were processed through MATLAB R2022b to enhance the flow structures. The shock cell length of the Chevron nozzle is 18–21% lower than the base nozzle. In the highly over-expanded case, zero penetration chevrons haven’t provided significant flow changes. Axial vortices induced by the chevron resulted in lobed jet formation, which increased initial mixing near the nozzle exit. Far field acoustic measurements of baseline and chevron nozzles were carried out, and inferences were made. Optimum noise reduction was obtained at the nozzle pressure ratio (NPR) 2.7 (over-expansion), with a maximum SPL reduction of around 4.1 dB at 45°. In an under-expanded case, the expansion of the jet enhances the performance of the chevron. This resulted in maximum noise reduction at NPR 4.2, with a range of reduction of around 4.9 dB (at 45°) and 1.9 dB (at 60°) compared to the baseline nozzle. Thus, Chevron has been able to provide an optimum noise reduction in an imperfectly expanded case with a minimum expected thrust penalty, which can lead to a significant result for practical applications.

Air-pulsed columns are used for specific solvent extraction processes which require maintenance-free equipment. The design of plate internal impacts the hydrodynamics and mass transfer rate in air-pulsed columns. Most of the studies on air-pulsed column focus on two conventional plate internals, i.e. sieve plates and disc and doughnut plates. In this study, a novel design of plate internal—linear slotted plate—is conceptualized. Linear slotted plates are characterized by 3 mm wide linear slots provided on a circular plate. Single-phase hydrodynamics and axial dispersion in air-pulsed column having linear slotted plate internal is reported. A comparison is done with disc and doughnut plate internal. A 3D CFD model of a 3 inch diameter column is reported. The open-source CFD software (OpenFOAM v10) has been used in the study. The numerical solution is obtained in two steps. Firstly, hydrodynamics (flow field) is predicted using pimpleFoam solver. Secondly, a snapshot approach is used to determine axial dispersion coefficient in the column. In this case, the velocity/flow fields obtained in the first step at two different instants of pulsing cycle are used to solve species transport equation. Axial dispersion coefficient is obtained for both flow fields and the overall axial dispersion coefficient is taken as arithmetic average of the two. scalarTransportFoam solver is used for solution of species transport equation. Step-1 is validated with the reported experimental data on local time varying velocity in a disc and doughnut pulsed column while scalarTransportFoam used in step-2 is validated against analytical expression. Axial dispersion is found to be less in linear slotted plate internal vis-à-vis disc and doughnut plate internal.

The global stability analysis is presented for the boundary layer on a thin, long circular cylinder aligned with a free-stream under the effect of suction and injection. A steady, two-dimensional laminar base flow solution is obtained by OpenFOAM software. The two-dimensional temporal stability equations are obtained by standard procedure from the equation of motions for incompressible flow in cylindrical coordinates. The spectral method is employed for spatial discretization of the stability equations. The eigenvalue problem (EVP) is established by formulating the stability equations along with appropriate boundary conditions in both the streamwise (x) and radial (r) directions. The EVP is solved using the Arnoldi iteration method, specifically implemented through the ARPACK package. The findings of an axisymmetric boundary layer (ABL) and a flat-plate boundary layer (FBL) are compared and found that transverse curvature strongly stabilizes the cylinder boundary layer. Also, ABL is found modally stable due to suction, while the boundary layer instability occurs because of injection even though Reynolds number (195) and intensity (0.5% of $$U_{\infty }$$ U ∞ ) are very small. The 2D spatial framework of temporal modes shows the wave packets are suppressed due to the suction and amplified due to the injection.

Fluid passing through penstock undergoes several types of flow losses including frictional and bend losses. In addition to this, a misalignment in penstock also contributes to total flow or pressure loss. Further, the possibility of material damage due to fatigue failure is also induced by the penstock misalignment. In this study effect of several penstock misalignments (0, 2, 4, and 6 mm) on pressure loss is numerically investigated using ANSYS Fluent software. Further, the region of stress concentration is obtained through fluid-structure interaction (FSI). The pressure loss in penstock with 6 mm misalignment is 1.3 times that of the pressure loss in perfectly aligned penstock. The paper suggests proper inspection of penstock misalignment in regular time intervals for the effective operation of hydropower plants.

In the present work, a numerical investigation of a square skewed cavity with an open top is performed. The results reveal the presence of mild convective motion around the upper corner of a cavity for low Rayleigh numbers. Formation of conduction layers is also found indicating conductive heat flow through fluid layers. Temperature gradient and stratified layers interaction govern the onset of natural convection. The numerical simulation is performed for the different skewness at angles of 30°, 45°, and 60°. Among these three angles, the intermediate skewness gives better results in terms of the local Nusselt number.

This study focuses on the multiphysics modelling of a classical alkaline water electrolyzer (AWE). An Euler–Euler two-fluid model is solved in addition to current conservation equations to tackle the problem. The objective is to investigate the effect of gas generation on the V–I characteristics of the system. The model is validated by comparing the model predicted V–I characteristics with available experimental data at different temperatures in a classical AWE. The study reveals that presence of gas increases over potential and reduces the current density. A special case with corrugated electrode is tested using validated model, and results are compared. Results indicate that these modification on electrode surface reduces the electrolyzer performance and current density which ultimately reduces hydrogen production rate. Hence it is essential that the electrodes are free of surface defects.

The liquid film thickness plays a crucial role in various engineering for heat and mass transfer applications. Dynamic studies are required to evaluate experimental performance and optimize operating conditions based on flow rate, longitudinal variation, temperature, and surface modification. This study used dynamic film thickness measurement on an inclined plate with and without surface modification. The inclined plate was layered with copper metal foam having 50 PPI and a thickness of 0.1 cm. The film thickness characteristic over the inclined plate was studied dynamically with respect to time, it was observed that for a higher flow rate, the film thickness fluctuations were higher compared to a lower range of flow. While the effect of flow rate ranging from 0.4 to 1.8 lpm on film thickness was examined, the film thickness increases with an increase in flow rate. The metal foam used in this study resulted in tortuous flow, detachment, and reattachment of the boundary layer, leading to better intermixing. The film thickness variation along the length of the plate with distances ranging from 0–20 cm was plotted. It was found that the film thickness increased up to 5 cm along the length of the plain inclined plate and up to 10 cm for the metal foam layered inclined plate. The copper metal foam gave uniform spreading on the surface, enabling it to operate at a lower flow rate than a plain inclined surface.

The following study investigates the behavior of flow when a solid cylinder, bluff body of diameter = 0.2* inlet height of the jet is introduced at the sudden expansion channel. The expansion ratio (ER = expanded channel height/inlet height of jet) of this channel is ER = 2. The cylinder is placed at the orifice of the expanded channel, i.e. at x = 0 and y = 0. The ordinary sudden expansion with symmetric expansion exhibits pitchfork bifurcation and a cylinder in a flow exhibits an unsteady Hopf bifurcation. But introducing a cylinder will lead to the occurrence of both the bifurcation instabilities at different ranges of Reynolds number Re. Both the bifurcations are observed at different Reynolds numbers. Through this study, it is discovered that Hopf bifurcation is ceased at higher Re than the pitchfork bifurcation. Though the pitchfork bifurcation shows asymmetry in the flow at critical Reynolds number Rec, due to the introduction of the cylinder this critical Reynolds number is increased by more than 10%, hence enhancing the stability of sudden expanded channel at higher Reynolds number. Mesh dependency has also been conducted in order to recognize relevant mesh size in order to produce accurate results and also optimize computational time and cost.

The increase in global energy demand fuelled by the increase in global population along with the need for sustainable and environment-friendly methods of electricity generation has shifted the focus to renewable sources of energy. One such form of energy is the wind energy. It is important to achieve the best possible performance from wind turbines to extract maximum amount of energy from the wind flow. This research work aims at designing a small-scale Vertical Axis Wind Turbine (VAWT) with suitable blade pitch control which would be useful in improving its performance. A three-bladed H-type Darrieus VAWT is considered with the NACA0021 airfoil as the blade cross-sectional profile. The pitch angle is made to vary sinusoidally with the position of the blade with respect to the direction of wind flow. The pitch angle amplitude used is 16°. A four-bar mechanism in the double crank configuration has been designed to implement collective blade pitching. Computer-aided design (CAD) models for various parts of the VAWT and the four-bar mechanism have been developed. The designs of these parts were found to be safe based on finite element analysis (FEA) carried out in ANSYS.

Air pulsed columns have proved to be the workhorse in nuclear reprocessing industry. Column internal design significantly affects the hydrodynamics and mass transfer rate in air pulsed columns. The majority of research in this field focuses on two commonly used plate internals: sieve plates and disc and doughnut plates. In this study, couple of novel designs of pulsed column internals named helical insert and baffled helical insert are reported. A 3D CFD model has been developed and hydrodynamics in each of these novel inserts/internals compared numerically. The computational approach involves solution of Reynolds-averaged Navier–Stokes (RANS) equations along with realisable k-ε turbulence model for single-phase flow. The CFD-based approach has been validated with reported experimental data on axial velocity at a point in a pulsed disc and doughnut column (PDDC). Once validated the model is used to quantify key hydrodynamic features like recirculation zones, streamlines and pressure gradients. These features are compared for both designs of helical insert, and inferences are drawn so as to how these novel inserts affect pulsatile flow fields.

This work examines the basic issue of magnetic fluid flow in a lid-driven cavity under the influence of a constant localized magnetic field. The magnetohydrodynamics (MHD) principles are consistent with the mathematical treatment of the problem. The magnetic fluid is viewed as a homogeneous Newtonian fluid that exhibits magnetization and is electrically non-conducting. The continuous partial differential equations are discretized using the second-order finite volume method (FVM) for the numerical solution using the free and open-source C++ program OpenFOAM version 10. Solver ferroSimpleFoam is created as a modification and development of the built-in solution simpleFoam. This solver is changed into a new program that may be used to study the dynamics of ferrofluid flow under the influence of an external magnetic field. Results pertaining to velocity show a significant influence of the magnetic field on the flow field.

The current study presents the effect of slip on the linear stability analysis of Newtonian fluids flowing in two layers within an infinitely long 2D channel. This two-layer flow system involves the mass transfer of species from the upper fluid layer to the lower fluid layer, with the upper wall having a more constant concentration of species compared to the lower wall. In this setup, the lower wall of the channel is treated as a slippery surface. The analysis focuses on the effect of slip on the Marangoni instability by implementing a slip condition on the lower wall of the channel. The results reveal that the application of slip to the lower wall of the channel can effectively regulate the stability of the two-layered flow system in the presence of soluble species.

In this article, we explore the phenomena of high-speed compressible boundary layer transition, laying the foundation for the development of advanced transition prediction models applicable to airflow over high-speed airfoils. Here, 2D spatial linear stability analysis (LSA) of the isothermal, compressible boundary layer over a flat plate is studied. The LSA technique is analysed by non-dimensionalisation, linearisation and Fourier-Laplace transformation of governing equations of flow. Compound matrix method (CMM) helps to remove the equation stiffness by creating all possible combinations from the original system. CMM equations are solved using the Runge–Kutta algorithm of the fourth order. Our study reveals the existence of numerous unstable modes associated with eigenvalues derived from the characteristic equations. Stability curves are obtained which highlights the complex behaviour of flow stability in the boundary layer. Moreover, the stability curves for cold and hot isothermal flat plate corresponding to both subsonic and supersonic flows are analysed. For Mach number $$M=0.6$$ M = 0.6 , the ratio of wall temperature to free stream temperature $$g_{0w} = 0.8$$ g 0 w = 0.8 and 1.4 are studied. Whereas for $$M=2.0, g_{0w}= 0.8, 1.6$$ M = 2.0 , g 0 w = 0.8 , 1.6 and 2.0 are studied. For the supersonic cold plate, wall temperature to free stream temperature corresponding to value 0.8, no unstable region is found till Re = 2000 and frequency( $$\omega _r$$ ω r ) ranging from 0.01 to 0.2. Notably, the critical Reynolds number exhibits an increasing trend when we transition towards colder surfaces, resulting in a reduction of the unstable area. These findings offer valuable insights into the intricate interplay of factors influencing boundary layer stability, especially concerning temperature differentials, thus contributing significantly to our understanding of transition in compressible flows.

The atmospheric boundary layer (ABL) flow over a smooth-to-rough surface heterogeneity is studied using large eddy simulation (LES). Two wall models are evaluated which prescribe the wall shear stress at any instant of time as a function of the velocity field at the first grid point away from the wall. The first Bouzeid (BZ) model locally applies the similarity theory using the twice-filtered velocity field. The second Abkar (APA) model blends the upstream and downstream profiles with a blending function. The wall shear stress is very sensitive to the wall models used, whereas the other flow statistics such as mean streamwise velocity, total shear stress (TSS) and turbulence intensity (TI) are insensitive. The LES data for these flow statistics agrees with the experiments up to a certain downstream distance behind the surface roughness jump. The internal boundary layer (IBL) heights obtained from the TSS or TI profiles in the experiment are much higher than those obtained from the LES. This suggests that the IBL relation that is given as an input in the APA model should be modified to match the experiment.

In the present study, three-dimensional numerical computations are performed on flow past a transversely rotating sphere at Re = 300 using OpenFOAM. Four values of the non-dimensional rotational speed ( $$\omega^{*}$$ ω ∗ ), viz. 0, 0.1, 0.3 and 1, have been chosen. Hilbert spectrum is plotted for lift force signal to examine the nonlinearity associated with the wake for different values of $$\omega^{*}$$ ω ∗ . Nonlinearity in the wake is found to be highest at $$\omega^{*} = 1$$ ω ∗ = 1 . A comparison is also made between the Fourier and the marginal spectra for different values of $$\omega^{*}$$ ω ∗ . DMD analysis has been carried out to compare the spatial and the temporal behaviour of the coherent structures in the flow for $$\omega^{*}$$ ω ∗ values of 0.3 and 1. Flow at $$\omega^{*} = 1$$ ω ∗ = 1 is found to be more stable than $$\omega^{*} = 0.3$$ ω ∗ = 0.3 .

This paper explores a strategy for mitigating the undesired occurrence of pump intake vortex. It is not possible to completely eliminate the formation of free surface vortex. The present paper focuses on reducing its effects through the implementation and evaluation of multiple intakes. The volume of fluid (VOF) approach is adopted for multiphase flows since it involves the interface between two immiscible fluids water and air by calculating the volume fraction of each fluid in each cell of mesh. Numerical results are validated using experimental results, and a comparison is made between scenarios with and without the multiple intakes approach. The analysis encompasses various models, including laminar, Standard k − ω CC, and SST k − ω CC, with their outcomes analysed and validated using experimental results. The numerical validation demonstrates that the laminar case closely matches with the observed results, and as the number of intakes increases the gas core length keeps on reducing which hence decreases the effect of free surface vortex. The study suggests the effectiveness in suppressing the vortex formation by increasing the number of intakes.

For years, fluid physicists have confounded over Rayleigh–Taylor Instability’s mixing layers. Rayleigh–Taylor (R.T.) instability is a well-known hydrodynamic phenomenon with applications in various scientific and engineering fields. This study comprehensively investigates R.T. instability using advanced Computational Fluid Dynamics simulations. The study begins with a detailed review of the theoretical background and the equations governing the R.T. instability. Numerical simulations are carried out to study the fundamental aspects of R.T. instability, including the influence of different physical parameters such as density ratios, Atwood numbers, and surface perturbations on the instability growth rates and characteristic wavelengths. Furthermore, the study delves into the implications of R.T. instability in various engineering scenarios, including mixing in multiphase flows, fuel sloshing in aerospace vehicles and plasma-fluid interaction in stars. The outcomes of this research will deepen our understanding of R.T. instability and pave the way for developing advanced predictive models and engineering strategies to control and exploit this phenomenon for practical applications. The knowledge gained from this study holds immense potential for enhancing the efficiency, safety, and performance of a wide range of fluid systems and processes.

The present study investigates flow characteristics of two-dimensional (2D) vortex-induced vibrations (VIV) of the flow past an elastically mounted circular cylinder using OpenFOAM. A low value of Reynolds number (Re = 150), a zero value of damping coefficient (ξ = 0) with a low value of mass ratio (m* = 2) have been taken to examine the wake characteristics for a fixed range of reduced velocity (Ur), ranging from 3 ≤ Ur ≤ 8. Vorticity contour has been presented to study the vortex shedding pattern behind the cylinder and unsteady wake flow for different values of Ur. Amplitude responses, synchronization regime, and time series of amplitude of transverse oscillation corresponding to lift coefficient (Cl) for different values of Ur have been studied. Hilbert spectral analysis has been used for unsteady periodic oscillations and to find the effect of Ur on wake transition for the signal of transverse velocity in the wake. Marginal and Fourier spectra have been used to analyze the frequency of wake-shedding, and it also helps to analyze the distribution of wake-shedding frequency in energy frequency domain. A comparison of the two spectra illustrates that even the lowest frequency can be extracted by using marginal spectra, which otherwise cannot be captured in Fourier spectra. Changes in the mean drag (Cdmean) and lift coefficients (Clrms) for different values of Ur have also been reported.

We study the stability of a thin liquid film on a heated, slippery slope, considering the impact of disregarding time-reversal symmetry, which introduces odd viscosity. Our theoretical model incorporates odd viscosity, slip length, and temperature-dependent surface tension, while also accounting for variations in liquid density with temperature differences. We study the impact of long-wave instabilities by deriving an evolution equation on the local film thickness. Linear stability analysis employing the method of normal modes shows that the slip length destabilizes the flow while a reduction in density stabilizes it. Furthermore, the presence of odd viscosity strengthens the stabilizing effect resulting from density reduction. Employing weakly nonlinear stability analysis with multiple scales, we find that certain wave numbers exhibit a supercritical bifurcation while others display a subcritical bifurcation. Numerical simulations in a periodic domain confirm the predictions made by the linear and weakly nonlinear analyses.

Experimental studies on vortex-induced vibration of bluff bodies require linear springs and air bearings for constrained and frictionless motion. The cost of air bearing system is high, and moreover, it needs a constant supply of pressurized air. We have devised an alternative, low-cost method to study experimentally the vortex-induced vibration characteristics of a single circular cylinder. A cantilever beam can be used to provide elastic support to the bluff bodies in place of springs and air bearings. The cantilever beam can also provide the restoring force and frictionless motion of the bluff bodies. The support of the cantilever beam can be either in the upstream or downstream direction relative to the cylinder. The cantilever’s length, width, and thickness are 540 mm, 30 mm, and 1.6 mm, respectively. The aspect ratio of the circular cylinder is 31. In this work, we have studied the effect of the direction of mounting of the cantilever beam on the VIV of a single circular cylinder. The peak of the highest vibrational amplitude of the circular cylinder, when the cantilever beam was mounted in the downstream direction, was recorded as $$A^*_{\max }=0.792$$ A max ∗ = 0.792 at $$U^*=6.1$$ U ∗ = 6.1 . The peak of the highest vibrational amplitude of the circular cylinder, when the cantilever beam was mounted in an upstream direction, was recorded as $$A^*_{\max }=0.74$$ A max ∗ = 0.74 at $$U^*=5.87$$ U ∗ = 5.87 . The peak of the highest vibrational amplitude of the circular cylinder in the case of the upstream circular cylinder attached to a cantilever is $$6.5\%$$ 6.5 % less than the downstream circular cylinder attached to a cantilever. The reduction in peak of the highest vibrational amplitude is due to the change in the direction of the moment of the drag force about the mean position of the cantilever beam.

Ensuring the safety of human spaceflight programs, particularly during the critical re-entry phase where the combination of high speeds and compression can result in temperatures well above 2000 ℃, is of paramount importance. In this context, the reduction of aerodynamic heating and the development of efficient thermal protection systems are crucial. In this study, active thermal protection system is envisaged, i.e., counterflow. The studies conducted by Hayashi, including both wind tunnel experiments (Hayashi and Aso in Effect of pressure ratio on aerodynamic heating reduction due to opposing jet. In: 36th AIAA thermophysics conference, p 4041, 2003, [1]) and numerical simulations (Hayashi et al. in Numerical study of thermal protection system by opposing jet. In: 43rd AIAA aerospace sciences meeting and exhibit, p 188, 2005, [2]), played a crucial role in uncovering the fundamental aspects of an opposing jet. In this project, the findings from Hayashi’s experiments were utilized to establish a basis for comparison and further analysis. The primary focus is on implementing an opposing jet within the crew module structure. A comprehensive numerical analysis is performed on the crew module, similar to that conducted on the blunt body, with a specific emphasis on studying the reduction in wall heat flux achieved through the implementation of the opposing jet.

The present work is an experimental study of two thin flexible sheets attached to the streamlined support, subjected to low subsonic flow. In the present study, two sheets made of OHP sheet with a constant aspect ratio attached to NACA 0015 aerofoils were studied at low-speed (0–15 m/s) by placing them in a side-by-side configuration. At low wind speeds, the sheets start oscillating at low-amplitude vibrations resulting in a large-amplitude flutter as the wind speed reaches a critical value. The critical Reynolds number depends on the gap between the filaments. Beyond this critical Reynolds number, the sheets are set to have two phases of oscillation, out-of-phase, and in-phase. The flow physics of the oscillating sheets was investigated through hotwire anemometry and particle image velocimetry (PIV).

Heat exchangers heavily rely on the flow channels as a key design aspect, making the optimization of flow channel design of paramount importance. Whenever reduced thermal resistance is desired, straight fins may be provided on the tube surface. However, in this comprehensive 3D computational study, the implementation of helical fins is thoroughly examined to further enhance the thermo-hydraulic performance of the system. In the pursuit of optimal designs, the fin pitch and helix angle are varied while keeping fixed operating conditions. The helix angle is varied from 5° to 25° with a step size of 5°, while the fin pitch spans from 1/5 to 1/30. Two different type of fin shapes, i.e., concave and convex, are considered. The results indicate that the helical fins offer substantial improvements in the thermal performance of the system. The study reveals that the thermal conductance significantly increases with the helix angle, showing a maximum enhancement of 754% and 806% for concave and convex fin geometries, respectively. Furthermore, the study indicates that increasing the fin pitch from leads to a deterioration in the thermal performance.

Indoor soot emission is a serious health problem in many industries. Indoor combustion is common in domestic as well as industrial applications. Indoor air contamination leads to non-communicable diseases like stroke, ischemic heart disease, lung cancer and chronic obstructive pulmonary disease according to WHO reports. Soot is a powdery mass made up of fine carbon particles. The main reason for soot is fossil fuel-based combustion. This research investigates the soot formation behaviors inside a SiC porous radiant burner (PRB). To numerically analyze the physical phenomena, mass, momentum and energy equations along with the soot formation mechanism based on a discrete sectional method have been employed. A premixed fuel-rich ethylene flame has been tested in this study, and the results for free flame and PRB have been compared. It was observed that in fuel–lean conditions, an appreciable amount of soot formation occurs in the PRB, whereas for fuel-rich conditions, the PRB helps in reducing the soot formation. The biggest soot particle diameter formed inside PRB was predicted to be around 19 nm smaller than the free flame case. This study also focuses on the soot formation behavior at various equivalence ratio conditions. It was numerically observed that the trend of soot volume fraction is significantly changed at around φ = 1.8. This study can pave the way to develop more effective burners in heavy industries including chemical processing, food and beverage industries, where indoor combustion is common.

This study investigates the oscillating behavior of a heavy pendulum in a vertical air jet. The behavior of a pendulum, initially inclined at a certain angle, is investigated under the influence of a jet with two distinct Reynolds numbers. A consistent observation is that with the increase in air jet Reynolds number (Re), the time taken by the pendulum to reach its vertical equilibrium state reduces. The air jet’s flow pattern, when deflected by the pendulum, creates a suction pressure that helps the pendulum return to its original position against the force of gravity. As the jet Reynolds number increases, the suction pressure becomes more pronounced, aiding the pendulum’s return to equilibrium. The subsequent effect is an increase in the frictional damping force experienced by the pendulum at its pivot, contributing to the observed behavior. A theoretical model is developed, and numerical results are obtained to support and validate the conclusion that the interplay between the suction pressure and frictional damping force is responsible for the observed reduction in the time taken to reach the vertical equilibrium state with the rise in air jet Re.

The fluid-structure interactions (FSIs) are challenging when the structures are flexible due to their intricate coupling nature. Numerical simulations of these interactions are even more challenging. Only in the recent days, there has been progress in the FSI solvers for such interactions. The solvers are validated at low Reynolds numbers against the numerical results. We consider an experimental investigation of flow behind square cylinder with flexible splitter filament at low Reynolds number which can be treated as a test case for numerical solver validation. We experimentally investigate the kinematics of a flexible splitter filament attached behind a square cylinder at $$Re_D =498$$ R e D = 498 in a soap film tunnel. The length of the flexible filament is L, and the side of the square cylinder is D. We varied the length of the filament from $$L^*= 1$$ L ∗ = 1 to $$L^*= 5$$ L ∗ = 5 , where $$L^*= L/D$$ L ∗ = L / D . Flow visualization using thin film interferometry and filament visualization were performed. The Fast Fourier Transform was performed on the time evolution of the tip locus to obtain the frequency spectrum. Detailed study on the frequency spectrum and the flow visualizations reveals that the filament length has a predominant effect on it’s kinematic behavior. For smaller length ( $$L^*= 1$$ L ∗ = 1 ), the filament tip oscillates with small amplitudes near the Mean Splitter Line (MSL). For $$L^*= 2$$ L ∗ = 2 , the filament reorients itself to one side of the MSL breaking the symmetry. From $$L^*= 3$$ L ∗ = 3 onward, the filament oscillates periodically and nearly symmetrically about the MSL. From $$L^*= 3$$ L ∗ = 3 to $$L^*= 5$$ L ∗ = 5 , the tip amplitude increases almost linearly with the length, whereas the tip oscillation frequency decreases. The vortex shedding frequency which is the same as the tip oscillation frequency decreases with increase in filament length ( $$L^*= 3$$ L ∗ = 3 to $$L^*= 5$$ L ∗ = 5 ).

Thermal convection in a two-dimensional circular enclosure is studied using long-time direct numerical simulations. We conducted an analysis on how the control parameters Ra and Pr influence the flow structures, global flow patterns, and heat transfer characteristics. To achieve this, we systematically varied the control parameters within the ranges of $$10^7 \le \text {Ra} \le 10^{10}$$ and $$0.1 \le \text {Pr} \le 15$$ . Unlike square convection cells, in the case of the circular convection cell, we observe three flow states: counterclockwise uniform circulation, chaotic state, and clockwise uniform circulation.

The paper investigates numerically the flow-induced vibration of both elastically mounted D-section and circular cylinder in tandem arrangement in the proximity and wake interference region at Reynolds number Re = 100. The problems are solved using in-house code based on level-set function-based immersed interface method (LS-IIM). Both elastically mounted cylinders have same diameter and mass ratio $$m^*$$ m ∗ = 2.0 with damping ratio $$\zeta $$ ζ = 0.005. The two cylinders are placed in tandem arrangement with varying gap ratios of $$G^*$$ G ∗ = 3.5–0.1. The circular cylinder is moved from wake interference region to proximity-wake interference region by decreasing the gap ratio. Our simulations reveal: (1) large amplitudes of vibration and wider lock-in for circular cylinder in tandem arrangement when compared to isolated; (2) over the range of $$G^*$$ G ∗ considered, the D-section cylinder shows both VIV and galloping response; (3) suppression of the galloping ability of D-section cylinder when the downstream cylinder at maximum proximity ( $$G^*$$ G ∗ = 0.1); and (4) three-stage transition of the vibration characteristics from VIV ( $$G^*$$ G ∗ = 0.1) to galloping (0.3 $$\le $$ ≤ $$G^*$$ G ∗ $$\le $$ ≤ 1.0) to wake-induced galloping ( $$G^*$$ G ∗ $$\ge $$ ≥ 2.0) of the downstream circular cylinder when the gap ratio increases. The three-vibration response has distinct flow dynamics occurring in gap, and each flow state is discussed in this paper.

In this study, the dynamics of gravity-driven shear thinning liquid rivulet falling over an inclined plane is assessed through numerical and experimental investigation. Instability in a fluid displacement is a complex phenomenon, governed by factors like three phase contact line, inclination, external body forces, fluid deformation and many factors yet to be completely resolved. Here, shear thinning fluid is modified with certain polymers and surfactants to enhance the wetting and also to understand the dynamics of instability by performing experiments and validate with the numerical 3D model. Cross flow model is referred to simulate the fluid and characterized using volume of fluid multiphase model. The simulation results were in comparable trend with experimental work for all the formulations with shear thinning fluid. Further, inclination angle is varied for both experiment and simulation to study the growth of instability and enhancement of wettability. On comparing both the results, 80% of the experiment data is closely in agreement with simulation.

A numerical investigation of two-dimensional (2D) flow inside a rectangular lid-driven cavity (RLDC) is performed, subjected to a vertical temperature gradient. The steady and unsteady nature of the flow in an RLDC is explored by solving the compressible Navier-Stokes equation (NSE) for two Reynolds numbers, Re = 4500 and 5500. In the setup, the bottom wall is heated with respect to the other three sides, which leads to a destabilizing vertical thermal gradient. Thus, there are two forced convection governing the flow: one due to the shearing action of the top lid and the other due to the thermal gradient imposed. The onset and propagation of the instability via the upper right corner of the domain are compared for the two Re considered. These show precessing vortical structures are reminiscent of supercritical flow inside a square lid-driven cavity. A primary core vortex is surrounded by gyrating satellite vortices, which remain in the flow field, even when a saturated state is achieved. Further, we explore the vorticity dynamics with time and the associated spectra, which reinforce the multi-periodic chaotic nature of the flow, irrespective of Re.

This paper presents a novel contactless air conveyor system, which has the potential to revolutionize material handling in various industries that utilizes air pressure differentials to transport planar objects without any physical contact. The system consists of a series of air chambers that create high-pressure air zones that move objects along a conveyor path. The advantages of this system over traditional conveyor systems include increase in efficiency, reduced maintenance requirements, and improved safety for workers. The design and operation of the contactless air conveyor system are described in detail, and experimental results demonstrate its effectiveness in transporting various types of objects. The primary goal of the current project is to create a smart, contactless conveyor that will allow things to move at extremely high speeds without ever encountering it. Here, we have taken all these issues related to the conveyor system into account and developed one of a kind futuristic conveyor concept that solves various problems. This system has the potential to revolutionize material handling in industries, where cleanliness, precision, and speed are critical factors.

A numerical simulation of one-way and two-way coupled FSI has been performed for a 2D rectangular cylinder situated in a water channel. The effect of flow velocity and aspect ratio (AR) on the rigid and flexible structures is investigated with the help of vortex-shedding frequency (f), velocity-swirling strength (λci), and total deformation (U). An accelerating-decelerating velocity field is applied to the flow field after the flow gets fully developed to observe the effect of wave impact on a rigid and flexible structure. The results have been compared for both domains to differentiate the flexible body from the rigid body. It has been found that by increasing the flow velocity, the f, λci, and U increase, whereas by increasing the AR, the U increases while the f and λci decrease. The study reveals that the Strouhal number (St) of the structure changes when we change the AR of the structure but remains constant when we change the flow velocity. The comparison of coupling shows that one-way coupling underestimates the structural deformation for low AR and high velocity but overestimates the deformation for high AR. In some cases, the solution of one-way coupling gives promising results equivalent to two-way coupling.

Presented article studies the secondary wake mode instability analysis behind a two-dimensional cylinder using OpenFOAM®. The instability of fluid flow is examined by obtaining the disturbance fields around the stable base flow solution. The objective of presented paper is to modify the existing icoFoam solver in OpenFOAM® to solve the linearized Navier–Stokes equation. The novelty of work lies in the utilization of an open source software—OpenFOAM® to predict the secondary wake (SW) instability around the base flow over two-dimensional circular cylinder. Modification of an inbuilt solver is done by altering the standard incompressible solver, i.e., icoFoam and its associated libraries to create a new modified solver named “stabilityFoam” (Code source link: https://github.com/ravikgpiit/stabilityFoam . The numerical simulation is investigated near secondary wake (SW) mode instability (Re $$\sim $$ ∼ 110.8) (Verma and Mittal in Phys Fluids 23(12):121701, [36]). In this regard, two Reynolds numbers are chosen as 100 (sub-critical) and 150 (supercritical). The stable base flow is simulated prior to the modified solver. We found that the flow shows stable transient energy growth characteristics for sub-critical Reynolds Numbers 100, while it is unstable and perturbations grow boundlessly at supercritical Reynolds number 150. The motivation of this study is to demarcate the secondary wake instability in flow over cylinder at sub-critical and supercritical Reynolds numbers utilizing OpenFOAM®.

The magnetohydrodynamic (MHD) instability of the liquid-liquid interface inside aluminium reduction cells is studied computationally. In aluminium reduction cells, conditions of the cell cavity, anode, and cathode assembly influence the distribution of electric current, and subsequently, the Lorentz force resulting in waves at the interface of molten aluminium and bath. The interface with pre-existing disturbances gets further perturbed by the scheduled operational activities in the aluminium smelter. Therefore, to study a practical scenario, a bichromatic perturbation with different wavelengths and independent wavenumbers along the cell length and width is considered here for the study. A 3D MHD model based on PHOENICS-ESTER is used to study the effect of cell length-to-width ratio. It is observed that, after an initial bichromatic perturbation, the amplitude of the interface oscillation increases with the increasing cell aspect ratio. However, in the case of a monochromatic perturbation, which is considered in most of the reported works, we see an opposite trend.

In order to accelerate the transition to a decarbonized energy future, hydrogen is gaining more and more attention as a flexible energy source. Future low-carbon power systems will rely heavily on gas turbines to maintain grid resilience and stability. A major shift in thermo-acoustic instability characteristics is observed when designing gas turbine combustors that run with either pure hydrogen or natural gas that has been enriched with hydrogen. Due to its greater reactivity and burning rates, it exhibits various thermo-acoustic instability features. In this paper, the flame stabilization mechanism for three hydrogen-blend fuels, pure hydrogen (PH), synthesis natural gas (SNG), and syngas (SG) for the turbulent bluff body combustor has been examined numerically. ANSYS Fluent 2022 R1 is used for numerical modelling of the turbulent non-premixed flames. The standard k-epsilon realizable model of turbulent flow and the probability density function (PDF)/Mixture Fraction combustion model for non-premixed combustion have been used in this study for the combustion modelling. The jet momentum flux ratio (MFR) and equivalence ratio (ϕ) both affect the flame stabilization with variation in Reynolds number (Re). It has been observed that PH flame is anchored very close to injection holes, SG flame stabilizes close to the walls of the combustor and in the shear layer of the bluff body, whilst SNG flame is observed in the shear layer and in the wake of the bluff body.

We present a smoothed particle hydrodynamics (SPH) simulation of two-dimensional fluid flow through a plain microchannel. A constant wall heat flux is applied to the walls of the microchannel, and the corresponding heat transfer is evaluated for different concentrations of nanofluids for different Reynold’s numbers (Re). The addition of nanoparticles in the fluid increases the heat transfer.

A computational study that aimed to predict the heat transfer (HT) and ablation rates for carbon/carbon composite, epoxy resin, and hydrated magnesium sulphate (HMS) in a hypersonic environment is presented. The motivation for this work lies in the importance of accurate modelling for designing and improving the performance of hypersonic vehicles. The high temperatures and pressures experienced during hypersonic flight can cause severe thermal stresses on the vehicle, leading to material degradation and failure. Therefore, accurate prediction of heat transfer and ablation rates is essential for ensuring the safety and performance of these vehicles. Towards this end, we have developed and validated a fluid-thermal-ablation coupling model that can accurately predict the heat transfer and ablation rates in a hypersonic environment. The study demonstrates that the model can be used to improve the design and performance of hypersonic vehicles by providing accurate predictions of thermal stresses on the vehicle. The study also highlighted the importance of accurate modelling for ensuring the safety and performance of hypersonic vehicles.

This paper presents a detailed experimental investigation aimed at comprehensively studying the mixing and screech tone characteristics of a rectangular jet subjected to fluidic injection. The primary objective is to analyze the influence of varying the mass flow rate ratio (Cm) between the fluidic injector and the main jet, as well as the expansion ratio (Pe/Pa) of the main jet, on the screech tone phenomena and mixing behavior of the jet. Extensive acoustic measurements are conducted to assess the impact of different flow conditions on screech noise generation. Additionally, pitot measurements are performed to investigate the variations in jet pressure profiles, providing crucial information regarding the jet’s dynamic features and the effectiveness of fluidic injection in reducing the core length of the jet, (L∗). Schlieren flow visualization techniques are employed to study the evolution of the jet’s shock structures and reveal the underlying flow physics. The experimental results demonstrate that the mass flow rate ratio (Cm) plays a vital role in governing the screech tone characteristics, with distinct frequency and amplitude variations observed for different Cm values. Moreover, the expansion ratio (Pe/Pa) significantly affects the screech tone frequency and exhibits a direct correlation with the jet’s shock cell structure. The findings contribute valuable insights into the screech tone phenomenon and its dependency on key flow parameters.

The purge air from the compressor in the form of bleed air is injected into the mainstream flow to prevent hot air ingestion in the wheel space. This purge flow mixes with the mainstream flow and increases the secondary flow losses by altering the flow structures near the endwall, thus reducing the turbine efficiency. The research aims at incorporating endwall contouring on the blades to improve turbine performance and reduce secondary flow losses. The numerical prediction of the generic high-pressure transonic axial turbine with purge flow passage is considered for the study. The steady-state computational analysis is carried out using Ansys CFX, with SST k-ω as the turbulence model. The endwall fillet radius has been incorporated into the hub and the shroud profiles of the blades. The turbine performance metrics in terms of static entropy, temperature, blade loading, streamlines, and sealing effectiveness are evaluated and compared with a baseline reference configuration without endwall contouring. The endwall fillet reduces the secondary flow losses at the blades’ leading edge and increases the endwall cooling. The blade loading on the rotor blade decreases with the increase in the fillet radius.

In this study, a spatial spectral analysis of turbulent plane wall jets is conducted using two-dimensional particle image velocimetry (2D-PIV) at three different nozzle Reynolds numbers: 10,244, 15,742, and 21,228. To accomplish this, four cameras are positioned side-by-side, capturing the longest field of view in the study of wall jets. The obtained PIV fields are utilized to construct spatial spectra, aiming to understand the model spectral contribution to the variance of velocity fluctuations and Reynolds shear stress. The study reveals that the jet mode exhibits wavelengths that scale with the jet length scale, denoted as $$z_{T}$$ z T . This mode contains two dominant submodes with wavelengths of 5 $$z_{T}$$ z T and 2.5 $$z_{T}$$ z T respectively. In the region above, the velocity maximum, the presence of the jet mode is observed, while the region below it exhibits a robust bimodal behavior attributed to both the wall and jet modes.

In the present work, we study the elevated liquid jet injection strategy into supersonic crossflow and compare its characteristics with that of the conventional flush (wall) injection. A liquid water jet from a 1 mm diameter orifice was elevated from the bottom wall, and liquid was injected into the supersonic crossflow at a Mach number, $$M_{\infty } = 2.5$$ M ∞ = 2.5 . The mean jet/spray penetration height and standard deviation of the penetration height were quantified for both elevated and the flush injection strategy using shadowgraph technique for all experiment cases for momentum flux ratio (J) of 9.7. The jet spray images are acquired using Particle/Droplet Image Analysis (PDIA) technique for both injection strategies at streamwise location of x/D = 60 from the jet exit for J = 9.7 (D = 1 mm). The jet penetration height and the unsteady characteristics of spray plume were measured. The measurements show that there is significant reduction in jet mean penetration height and standard deviation for the elevated jet injection case compared to flush jet injection case. The qualitative differences seen in spray droplet size between the two injection strategies are highlighted.

The present study highlighted the control of wind velocity inside the different types of openings inside the tall building to harvest the wind energy and implement it for further use. A regular square plan-shaped tall building model of 1:1:4 (length: breadth: height) is considered for the comparative study between the other considered slot-type models. Other slot-type models are considered at different symmetric geometrical shape openings. The openings are contemplated at the upper portion of the models. The considered six models are also of 1:1:4 ratio. Only along wind flow velocity inside the opening is considered according to the shape of the opening geometry. After analysing the computational fluid dynamics (CFD) simulation, the study concluded some important points. The wind velocity inside the opening can be maintained according to the alteration of the geometrical shape of the opening. The minimum opening inside the model increases the velocity. Therefore, the wind energy harvesting devices can be placed at a particular location where the wind velocity increases according to the modified geometrical shape.

Intracranial aneurysms are anomalies near the bifurcations and curvatures in the cerebral circulatory system. The rupture of an aneurysm is a medical emergency with higher mortality rates. Understanding the disease initiation, progression, and rupture stages of an aneurysm is of clinical significance and valuable for patient management. However, this is greatly influenced by hemodynamic parameters, which can be obtained by computational fluid flow simulations. In the present study, the coupling between the fluid and arterial wall is resolved by accounting for the compliant nature of the walls by solving for both the flow field and structural dynamics. Patient-specific simulations are performed for a middle cerebral artery bifurcating aneurysm with three different elastic moduli (1 MPa, 2 MPa, and 3 MPa). FSI simulations reveal that an increase in elastic moduli results in reduced wall stresses and wall displacements with an attendant increase in fluid stresses. Rigid wall CFD simulations were found to overestimate the WSS values compared to FSI studies.

Particle image velocimetry flow measurement has been performed to measure the laminar boundary layer over an axisymmetric body. A torpedo-shaped model is used as an axisymmetric body. The Reynolds number based on the diameter of the body ‘D’ is varied from 3500 to 10,500. The boundary layer is tripped by a 2.5-mm nitrile rubber placed at 60 mm from the nose of the model to see its effect on the stability of the boundary layer. The laminar boundary layer gets disturbed by the trip wire and relaminarizes again to match the Blasius profile at Re = 3500. Whereas, for higher Reynolds numbers, the boundary layer undergoes a transition, and the velocity profile tends to obtain power law. The local coefficient of friction (C′f) is reported for laminar and transition boundary layer cases. The C′f distribution over the model is lowest for Re = 3500 and found to be lower than the planar laminar boundary layer case throughout the length of the model. The C′f  for higher Reynolds numbers is higher than the planar turbulent boundary layers for X/D ≤ 2.2 and lower for the downstream locations, which owes to the thickening of the viscous sub-layer.

Friction drag at the surface in atmospheric boundary layers (ABLs) is the most challenging flux quantity to infer from observations and simulations of mean wind speed profiles and requires an appeal to similarity theories. Recently, we have reported a new scaling framework and predictive model for drag in non-convective, smooth-walled laboratory turbulent boundary layers (lab TBLs) (Dixit et al. in Phys Fluids 32(4) [1]). Here, we evaluate this predictive model for a specific class of ABLs called truly neutral ABLs (TNABLs) through large-eddy simulations (LES). TNABL is free from convection effects at its upper as well as lower boundaries and therefore bears the closest correspondence to lab TBLs in that respect. From the viewpoint of testing scaling laws, TNABLs present attractive friction Reynolds numbers two to three orders of magnitude higher than the largest Reynolds numbers achieved in lab TBLs to date. The LES study reported here uses the weather and research forecasting (WRF) model in ideal simulation mode. Specifically, we attempt to understand the role of surface roughness in the LES of TNABLs toward the applicability of our predictive drag model. Our results show that the drag scaling and predictive model show promising potential to handle TNABLs provided that the roughness length typical of laboratory experiments is set for WRF simulations.

The present study investigates the acoustic characteristics of leading edge (LE) and trailing edge (TE) modified airfoils, which is compared with baseline un-serrated airfoil. The acoustic characteristics are investigated through an acoustic camera. The study shows uniform acoustic radiation throughout the span of the baseline airfoil, while the dominant radiation is seen from the root and tip sources of the LE/TE modified airfoils. Further, the flow visualization was done on baseline and LE/TE modified airfoils to understand the flow behavior and its connection with the acoustic radiation. It shows uniform flow over the span of the baseline airfoil, which indicates uniform acoustic radiation. The flow is not uniform throughout the span of the LE/TE modified airfoils which represents lower acoustic radiation. It can be concluded that the LE/TE modified airfoil could inhibit the spanwise growth of the vortices and reduces the radiation intensity.

Blast waves can cause serious injuries. Hence, significant research effort has been dedicated toward developing better and secure bunkers. Here, we investigate bunker design technique using the wire mesh. So, it is pertinent to study blast wave attenuation and mitigation. In laboratory settings, blast waves can be generated using shock tube. In the present study, shock waves are made to come out of the shock tube and collide with a wire mesh placed outside the shock tube. The shock attenuation happening on the wire mesh of different configurations for different Mach numbers and thereof variation in the flow are to be clearly understood. The study in this paper involves the finding of flow behavior across a rectangular sized wire mesh for a particular Mach number. Particle image velocimetry (PIV) is used for flow visualization and velocity and vorticity field are studied thereby. It is found that the strength of the shock wave is considerably reduced after passing through the wire mesh.

The present study aims to study the evolution of an inclined synthetic jet in a quiescent ambiance. The inclined synthetic jet is particularly useful in drag reduction and separation control applications. The synthetic jet is generated using cam-follower-based linear actuation through a $$30^\circ $$ 30 ∘ inclined circular orifice. The study has been conducted at Re = 232 and $$L/D = 1.3$$ L / D = 1.3 . The peak time-averaged velocity is skewed towards $$\psi = \pi $$ ψ = π side of the orifice. The ring has higher circulation towards $$\psi = \pi $$ ψ = π side, compared to $$\psi = 0$$ ψ = 0 side. During evolution of synthetic jet, it bends towards the $$\psi = 0$$ ψ = 0 side. The secondary structures are induced near the orifice, which induces a velocity that advects the ring towards the wall (orifice plate). The low circulation side of the ring further interacts with the wall and loses vorticity. The inclined synthetic jet has higher decay rate and limited penetration in the wall normal direction. The phase-averaging technique is used to study the evolution of the synthetic jet. The low-dimensional POD reconstruction is performed to extract the phase information from the PIV velocity measurement, and compared to direct phase averaging technique.

During lunar landing, exhaust from the retro-rocket strikes the lunar surface producing a shock close to the surface. The post-shock pressures near the lunar surface cause entrainment of dust in the plume, which may prove to be hazardous to the rocket. In the present study, the rarefied flow away from the lander nozzle is predicted using the Direct Simulation Monte Carlo (DSMC) method to investigate rocket-plume impingement on undulated surfaces to study the effect of surface roughness on plume movement. Comparative analysis with plume impingement on the flat surface shows that static pressure distribution along the lunar surface is uneven and peaks at crests on the undulations.

Amplitude modulation coefficient $$R_{\text {AM}}$$ R AM for the plane, turbulent wall jet (henceforth wall jet) data published by Gupta et al. (J Fluid Mech 891:A11 [1]) is computed using Hilbert transform method (a combination of Fourier and Hilbert transforms) and compared with the $$R_{\text {AM}}$$ R AM data from Bhatt and Gnanamanickam (Phys Rev Fluids 5:74604 [2]) at matching Reynolds numbers (Re $$_\tau $$ τ as well as Re $$_\delta $$ δ ). Discrepancies between the two curves are discussed with focus on lateral confinement of the wall jet. Wavelet transform method (a combination of Fourier and wavelet transforms) is also used to compute $$R_{\text {AM}}$$ R AM and validated against the Hilbert transform method calculations. Furthermore, wavelet transform method is used to compute the frequency modulation coefficient $$R_{\text {FM}}$$ R FM . Results for $$R_{\text {AM}}$$ R AM and $$R_{\text {FM}}$$ R FM computed for the three Re $$_j$$ j experiments reported by Gupta et al. (J Fluid Mech 891:A11 [1]) display Reynolds number similarity of the amplitude and frequency modulation in wall jets over the range of Reynolds numbers covered.

Wind energy has gained significant popularity as a renewable energy source, with horizontal axis wind turbines (HAWTs) being widely used for its efficient capture. The performance of HAWTs is greatly influenced by the design of their aerofoil blades, which convert wind energy into mechanical energy. To explore improvements in aerofoil aerodynamic properties, a basic research study was conducted using computational analysis. The study focused on the impact of different types of grooves on the surface of the NACA 23021 aerofoil. These grooves have the potential to enhance lift, reduce drag, and improve the stability of the aerofoil by promoting a more uniform pressure distribution. The grooves induce vortices in the fluid flow, enabling modification and control of flow direction and speed. This can lead to increased lift and decreased drag. Pilot studies on the 5-series aerofoil demonstrated reduced lift and drag coefficients at higher angles of attack (14°, 16°, 18°), with stall observed at 13° angle of attack (AOA). The study employed a segregated, implicit solver, k-ε SST model in ANSYS Fluent 2020. Unlike most published simulations, a multiblock organized grid was utilized, providing better accuracy, and capturing the curvatures of the leading and trailing edges through structured grid implementation. Analysis was conducted at 14°, 16°, and 18° angles of attack, considering parameters such as the ratio of boundary layer thickness (δ) to groove depth (h) (h/δ: 0.5–1.0) and groove depth (h) to groove width (d) ratio (h/d: 0.1–1). Among these conditions, the best improvement in lift-to-drag ratio, reaching 15.3%, was achieved at h/δ  = 1.0, h/d = 0.2, and a 16° AOA. The application of grooves on an aerofoil has proven to be a swift and effective technique for flow management, enhancing the performance of the aerofoil. It serves as a valuable tool for aerodynamic design and optimization, offering potential benefits such as increased lift, decreased drag, and improved stability.

The study focusses on optimising the cooling of lithium-ion batteries using a direct contact liquid-based immersion cooling system. Lithium-ion batteries are significantly influenced by the temperature with an operational limit of 35 °C and an inter electrode temperature difference less than 3.5 °C for prolonged service life. The paper uses a resistance-based energy model to simulate battery temperature during discharge, while cooling the arrangement using a commercially available dielectric. The study explains the vortex activity that occurs as the fluid traverses the battery module. The simulation reveals an undesirable thermal gradient over the cell surface due to the construction of the battery stack. To mitigate this effect, vortex generators (VG) are introduced that alter the flow behaviour and reduce the temperature difference formed on the battery surface. By altering the position of the vortex generators, the corresponding change in fluid behaviour, the vorticity magnitude, and the average Nusselt number is established. Two key indices: the cooling uniformity index and pumping power index are introduced to quantify the thermal gradient on the cell surface and the total pressure loss as the fluid flows through the system. The findings indicate that a middle-positioned VG produces the most favourable cooling index of 0.18 which corresponds to a maximum reduction in temperature difference of 1.65 °C and a pumping power index of 0.14 showcasing the most effective cooling performance.

Extensive experimental investigations of transonic flow development over the payload region of a generic launch vehicle model have been carried out. The effect of changing the semi-nose cone angle in the range of $$15^\circ $$ 15 ∘ to $$25^\circ $$ 25 ∘ is one of the problems studied. For angles of $$20^\circ $$ 20 ∘ – $$25^\circ $$ 25 ∘ and certain combinations of Mach number and angle of attack, a large amplification of pressure fluctuations was observed. This paper reports analyses of pressure sensor data and high-speed shadowgraph images based on the dynamic mode decomposition (DMD) technique to better understand the phenomena. This technique holds significance in flow diagnostics and the prospective estimation tools of complex nonlinear flow phenomena.

Earth tube heat exchangers (ETHEs) are sustainable systems that use the Earth’s stable temperature to condition incoming ventilation air, providing an energy-efficient solution for indoor climate control. This research project investigates methods to enhance air quality within ETHEs, focusing on the mitigation of potential air quality issues related to moisture and particulate matter. A custom-designed EAHE system was coupled with a dehumidification unit to treat the incoming air before it interacts with the ground heat exchanger. The dehumidifier employed desiccant technology, effectively reducing the moisture content in the incoming air stream. This modification not only enhanced the air's density but also mitigated the risk of condensation within the heat exchanger, which can lead to reduced efficiency and potential system damage. The study explores innovative technique of adding dehumidifier at the inlet to improve the overall indoor air quality and thermal comfort through the utilization of ETHE technology. Using a validated model in SimScale software, we conducted a comparative analysis of heat exchanger efficiency, taking a stepwise approach. The experimental phase of this study involved monitoring comparing with the predesigned model and analyzing the performance of the enhanced ETHE system. Results indicated a significant reduction in moisture levels within the ventilation air, which, in turn, increased the density of the air, and as a result, 3.82% increase in temperature difference was found. Additionally, adding dehumidifier will also help in reduction of corrosion of the system.

Natural convective flows are commonly found in nature around us in our day-to-day life such as in atmospheric and oceanic flows, electronic cooling, and building ventilation. Studying such flows within enclosures can provide important information about flow field which can help to explain transport of neutrally buoyant bio-aerosols, contaminants, etc. In this study, linear stability analysis of two-dimensional steady base flow inside a square cavity is carried out by considering three-dimensional disturbances. The 2D base flow has been numerically computed over the range of Rayleigh number, $${\text{Ra}} = 10^{4}{-}10^{5}$$ Ra = 10 4 - 10 5 , Prandtl number, $${\text{Pr}} = 0.71$$ Pr = 0.71 (air). The evolution equations of the perturbations have been obtained using linear stability theory, and using normal mode form of solution leads to a generalized eigenvalue problem (EVP). A mixed finite element P2-P1 spatial discretization was used to solve both the base flow and EVP. Temporal stability analysis was carried. The eigenspectrum for a particular case ( $${\text{Ra}} = 10^{4}$$ Ra = 10 4 , wave number = 1) is studied. In the parameter range $${\text{Ra}} = 10^{4}{-}10^{5}$$ Ra = 10 4 - 10 5 , the critical flow parameters, Ra values and corresponding wave numbers, at which the flow loses stability are determined.

Practical applications of various bent pipes often show turbulent flow. This work is done to study single-phase turbulent flow of water through a Z-bend pipe. The SST k-omega turbulence model is used to simulate the flow. Prior to simulation, the method was validated with published results in previous literature, and a good agreement was established between the designed and published results. The present work establishes that the pressure and velocity contours of the Z-bend carrying water remain the same for the considered range of Reynold’s number. The mean velocity tends to move from the inner part to the outer part of both the bends. However, the location of the points of separation at the lower and upper bends varies with Reynold’s number.

A synthetic jet impingement is a potential method for removing heat but currently has some specific challenges. One of the challenges is the low value of heat transfer compared to the steady jet impingement in confined spaces. The reason behind the lower performance is the recirculation of hot air from the heated surface. There is a need to change the flow structure to limit hot air recirculation. Therefore, the effect of rib location and size on heat transfer has been studied numerically. A numerical investigation on ribs (ring fins) has been carried out using square fins having height and width of 5 mm × 5 mm, 2 mm × 2 mm, and 1 mm × 1 mm at different nondimensional radial locations of r/d = 2, r/d = 1, and r/d = 0.5. An acoustically actuated synthetic jet is operated at 125 Hz with an orifice exit of 10 mm corresponding to Reynolds number 5473. It is found that adding a ring fin improves heat transfer at specific radial locations far from the stagnation point. Still, overall reduction has been observed due to confinement and backflow effects.

The pulsating jet impingement has been subjected to research to provide enhanced heat transfer. Still, there is quite a mismatch between the results provided by various studies display mixed heat transfer behavior. The reason behind the complex heat transfer behavior is still unclear. The current study uses acoustically driven pulsation chamber, which adds pulsations to the steady flow. A wide range of Strouhal number (St = 0–0.7) for different surface-to-nozzle spacings (z/d = 0.25–8) are studied for a constant Reynolds number (Re) of 3265 and pulsation amplitude (A) of 40%. The experimental setup is validated with existing steady jet impingement data with acceptable accuracy. The results of the experiments show that there is minor effect of the change in St for a particular value of z/d. The maximum change compared to the steady jet lies within ± 5%. At small z/d, the high kinetic energy of the jet dominates the flow behavior, and there is a peak formation away from the stagnation point. With increase in the z/d, the average heat transfer reduces. Results shows a trend that pulsating jet with a higher St at low z/d and lower St at high z/d provide better heat transfer performance, although the change is minimal.