Ashwani Assam - Academia.edu (original) (raw)

Papers by Ashwani Assam

Effect of rarefaction on thermal and chemical non-equilibrium for Hypersonic flow with different enthalpy and catalytic wall conditions

Journal of Thermal Science and Engineering Applications

Compressibility and rarefaction effect plays an essential role in the design and study of objects... more Compressibility and rarefaction effect plays an essential role in the design and study of objects experiencing hypersonic flows. The presence of chemical and thermal non-equilibrium in hypersonic flows increases the complexity of estimating aerothermodynamic properties, which are essential for developing thermal protection systems and the aerothermodynamic design of hypersonic vehicles. In this study, the hy2Foam solver, is used to understand the effect of Knudsen number (which in turn depends on the altitude) and free-stream enthalpy variation on the surface aerothermodynamic properties such as pressure, heat flux, velocity slip, temperature jump, and flow-field variables such as species concentration and temperature, in five-species air flow over a cylinder, for both noncatalytic and fully catalytic wall condition. The novelty of the work lies in reporting the effect of rarefaction on thermal and chemical non-equilibrium (associated with hypersonic flows), and thus on the surface ...

Physics of Fluids

The least squares and Green–Gauss gradient schemes have been traditionally studied as two distinc... more The least squares and Green–Gauss gradient schemes have been traditionally studied as two distinct techniques for gradient computation on unstructured meshes in the literature. In this Letter, we show that the Green–Gauss gradient method can be interpreted as a weighted least squares gradient scheme and that methods of the Green–Gauss family may therefore be encompassed in the larger set of least squares-based gradient schemes.

This paper reports a computational and theoretical investigation of pressure-flow characteristics... more This paper reports a computational and theoretical investigation of pressure-flow characteristics of a microchannel having a superhydrophobic bottom wall with embedded air-cavities and, thin deformable membrane as the top wall. Two-way fluid-structure interaction (FSI) and unsteady volume of fluid (VOF) methods are employed for fluid-solid boundary and liquid-air interface at ridge-cavity, respectively. A novel theoretical model has been developed for the pressure-flow characteristics of microchannel with deformable top and superhydrophobic bottom wall. The theoretical and numerical results for pressure drop across the microchannel have shown a good agreement with a maximum deviation of 6.69%. Four distinct types of microchannels viz, smooth (S) (rigid non-textured), smooth with deformable top (SDT), smooth with superhydrophobic bottom (SSB) and, smooth with superhydrophobic bottom and deformable top wall (SSBT) have been investigated for the comparison of their pressure-flow charac...

Evaluation of novel wall function approach for supersonic flow problems involving separations induced by geometry and shocks

Computers & Mathematics with Applications

Investigation of All-Speed SLAU Scheme in Incompressible Limit

Density-based algorithms are generally used to solve high-speed flows; the accuracy of these meth... more Density-based algorithms are generally used to solve high-speed flows; the accuracy of these methods degrades in low-speed limit i.e. in incompressible limit due to a large value of the condition number. A popular method to fix this issue is the use of preconditioning methods. Preconditioning not only maintains the accuracy in low Mach limit but also helps in accelerating the convergence by altering the characteristic speeds, which results in destructions of the time accuracy. Whereas new parameter free scheme has been suggested by Shima which solves the problem without destroying the time-accuracy. In this paper, we investigate the SLAU scheme of Shima in the incompressible limit for practical applications such as aerofoils at an angle of attack using our in-house developed 3-D unstructured hybrid code

A novel least squares finite volume scheme for discontinuous diffusion on unstructured meshes

Computers & Mathematics with Applications, 2021

Application of the K-KL Model to Engineering Flows

Proceeding of Proceedings of the 25th National and 3rd International ISHMT-ASTFE Heat and Mass Transfer Conference (IHMTC-2019), 2019

Computation of Rarefied Gas Flows in Nano/micro Devices using an Indigeneous Developed Computational Fluid Dynamics Solver

Gaseous Nano/micro Electronic Mechanical Systems (NEMS/MEMS) are used for measurement and control... more Gaseous Nano/micro Electronic Mechanical Systems (NEMS/MEMS) are used for measurement and control in the atomic level. Numerical simulation of such system is important for understanding the gas flow behaviour in such devices. Non-equilibrium effects such as small characteristic length, rarefaction and gas-surface interactions characterize such flow behaviour. The Knudsen number, Kn, ratio of the molecular mean free path, λ, to the characteristic length of the geometry, l is used to characterize the translational non-equilibrium of a rarefied gas flow in nano/micro devices. For high gas density with small Kn (Kn≤0.001) the conventional Navier-Stokes (NS) equations are applicable. When the gas density becomes small, the mean free path of gas becomes large and the non-equilibrium effects appear in the flow with fewer collisions between molecules. The conventional NavierStokes equation with velocity slip and temperature jump conditions can be used to simulate the slip-flow regime 0.001≤...

We carry out numerical simulations to optimize the re- entry capsule configurations based on aero... more We carry out numerical simulations to optimize the re- entry capsule configurations based on aero-thermodynamic properties such as drag, pressure and heat load. The open source software OpenFOAM is used with the compress- ible computational fluid dynamics (CFD) solver rhoCen- tralFoam. CFD solver is implemented with the first-order Maxwell’s velocity slip and the Smoluchowski temperature jump boundary conditions. We report results for different altitudes and Mach numbers with varying second cone an- gle and bluntness of the re-entry capsule. It is noted that the heat loads are greatly reduced by changing the capsule con- figuration from single to bi-cone. With increasing second cone angle heat loads are enhanced, but the average drag and pressure coefficients found to be least sensitive. How- ever, with increase in bluntness the average value of heat load decrease slightly and the peak value significantly, while drag values exhibit contrasting behaviour.

Turbulent mixing is highly a ected by uid compressibilty. The current work aims to study the e ec... more Turbulent mixing is highly a ected by uid compressibilty. The current work aims to study the e ect of compressibility corrections for 3 di erent Reynold Averaged Navier Stokes (RANS) turbulence models namely the standard k-epsilon, RNG and Spalart Allmaras models using an in-house parallel three dimensional unstructued CFD solver to compute a high speed mixing layer. The experimental study done by Goebel and Dutton has been used as the benchmark for investigation. The standard kis compared with the RNG model to see the e ect of the change in model coe cients on the predicted ow physics. The one equation Spalart Allmaras model is compared with the aforementioned two equation model to make the performance comparison complete. Turbulent quantities like rate of mixing layer growth, turbulence intensity and normalized Reynold's stress have been compared with benchmark results along with mean ow quantities like the self similar velocity pro les and their results have been presented.

Use of the Pressure Jump Boundary Condition in the High Speed Rarefied Gas Flows

The simulation of rarefied gas flow in hypersonic aerodynamics is important for the design of spa... more The simulation of rarefied gas flow in hypersonic aerodynamics is important for the design of space and re-entry vehicles. Computer simulations can provide the necessary aerodynamic data at less cost and for cases where experiments are difficult to conduct. Therefore, there is a constant effort to develop newer numerical methods and to improve the existing ones based on appropriate physical modeling, so as to make the computer simulations closer to reality. CFD methods are preferred for rarefied flows in the continuum and slip flow regime. The range 0.001 ≤ Kn ≤ 0.01 is called the slip regime, where the no-slip conditions are no longer applicable. The no-slip boundary conditions are replaced in this regime with slip velocity and temperature-jump boundary conditions.

Computational aerothermodynamics is the branch of science which focuses on the computation of the... more Computational aerothermodynamics is the branch of science which focuses on the computation of the effect of thermodynamic and transport models on aerodynamics and heating. They are widely used for external ow cases. On the other hand, the computation of heat and stress in the design of Nano/Micro Electronic Mechanical Systems from the point of view of a Fluid mechanics engineer is also an important area of study. A generalized computational tool which can simulate the low and high speed flows at both the macro and micro levels is desirable from the perspective of industry, academics and research. For a developing nation, it is extremely important to have such a solver developed indigenously to create self-sufficiency and self-reliance. In this work, a robust three-dimensional density-based general purpose computational fluid dynamics solver was developed in house by our research group. The cell centred finite volume discretization method is used on an unstructured grid, which is mor...

Adaptive time-stepping is a method of choosing a variable time-step size for time-marching applic... more Adaptive time-stepping is a method of choosing a variable time-step size for time-marching applications given prescribed tolerance for local error. When applied to steady-state problems this method acts as a convergence accelerator while for transient problems it maintains the time accuracy using a user-prescribed error criterion. In this paper, we demonstrate the usefulness of this method over the commonly-used CFL based time-stepping for different problems with steady/unsteady laminar viscous flow.

Effect of recirculation zone on debris evacuation during EDM deep hole drilling

Procedia CIRP, 2021

International Journal of Numerical Methods for Heat & Fluid Flow, 2020

Purpose The purpose of this study is to present and demonstrate a numerical method for solving ch... more Purpose The purpose of this study is to present and demonstrate a numerical method for solving chemically reacting flows. These are important for energy conversion devices, which rely on chemical reactions as their operational mechanism, with heat generated from the combustion of the fuel, often gases, being converted to work. Design/methodology/approach The numerical study of such flows requires the set of Navier-Stokes equations to be extended to include multiple species and the chemical reactions between them. The numerical method implemented in this study also accounts for changes in the material properties because of temperature variations and the process to handle steep spatial fronts and stiff source terms without incurring any numerical instabilities. An all-speed numerical framework is used through simple low-dissipation advection upwind splitting (SLAU) convective scheme, and it has been extended in a multi-component species framework on the in-house density-based flow sol...

Performance of thek-kLmodel for aerodynamics applications

International Journal of Numerical Methods for Heat & Fluid Flow, 2019

PurposeThe purpose of this paper is to study the predictability of the recently proposed length s... more PurposeThe purpose of this paper is to study the predictability of the recently proposed length scale-based two-equationk-kLmodel for external aerodynamic flows such as those also encountered in the high-lift devices.Design/methodology/approachThe two-equationk-kLmodel solves the transport equations of turbulent kinetic energy (TKE) and the product of TKE and the integral length scale to obtain the effect of turbulence on the mean flow field. In theory, the use of governing equation for length scale (kL) along with the TKE promises applicability in a wide range of applications in both free-shear and wall-bounded flows with eddy-resolving capability.FindingsThe model is implemented in the in-house unstructured grid computational fluid dynamics solver to investigate its performance for airfoils in difficult-to-predict situations, including stalling and separation. The numerical findings show the good capability of the model in handling the complex flow physics in the external aerodyna...

Journal of Turbulence, 2019

Spalart-Allmaras (SA) model is a low Reynolds number (Re) model, which means that the first off-w... more Spalart-Allmaras (SA) model is a low Reynolds number (Re) model, which means that the first off-wall grid point should be placed in the viscous sub-layer with y + 1. This restriction of placing the first off-wall grid point so close to the wall leads to an increase in the mesh size, and thus the computation. The wall function approach is an alternative to this problem. The standard wall function method usually employed has a limitation for cases that involve high adverse pressure gradient and compressibility. This limits its use to the nonseparated flows only. The present work focuses on the formulation of the generalised wall function given by Shih et al. [A generalized wall function; 1999] and applies it to the SA turbulence model, with some modification. The proposed modification was found to remove the oscillation and inaccuracy found in the result when directly using the Shih et al. model. Several flows, with zero pressure gradient to those with adverse pressure gradient leading to flow separation, are solved with the proposed wall treatment, with relatively coarse grids involving y + beyond 50 and up to 100 for certain cases. It is concluded that the results in each case are close to those obtained by the low-Re SA model, despite the use of much coarser meshes.

A Numerical Study of Shock and Heating with Rarefaction for Hypersonic Flow Over a Cylinder

Journal of Heat Transfer, 2019

The numerical computation of hypersonic flows over blunt bodies is challenging due to the difficu... more The numerical computation of hypersonic flows over blunt bodies is challenging due to the difficulty in robust and accurate wall heat flux prediction and proper capturing of shock waves free from the ``carbuncle" phenomenon and other shock anomalies. It is important to understand how these behavior is affected due to rarefaction, which in turn will help to improve the study of aerospace vehicles flowing in rarefied and hypersonic regime. Recently, the SLAU2 convective scheme was shown to suppress the shock anomalies found in capturing strong shocks, however, it still showed a wavy pattern of heating. We have proposed a modification to the SLAU2 convective scheme to improve the accuracy of flow predictions in the presence of strong shocks. We then perform the numerical simulation of hypersonic viscous flow over a cylinder at Mach 888 and 16.3416.3416.34 at different Knudsen numbers. We carry out the study using the modified SLAU2 and the classical Roe schemes. We study how the shock ano...

International Journal of Numerical Methods for Heat & Fluid Flow, 2019

Purpose Accurate prediction of temperature and heat is crucial for the design of various nano/mic... more Purpose Accurate prediction of temperature and heat is crucial for the design of various nano/micro devices in engineering. Recently, investigation has been carried out for calculating the heat flux of gas flow using the concept of sliding friction because of the slip velocity at the surface. The purpose of this study is to exetend the concept of sliding friction for various types of nano/micro flows. Design/methodology/approach A new type of Smoluchowski temperature jump considering the viscous heat generation (sliding friction) has recently been proposed (Le and Vu, 2016b) as an alternative jump condition for the prediction of the surface gas temperature at solid interfaces for high-speed non-equilibrium gas flows. This paper investigated the proposed jump condition for the nano/microflows which has not been done earlier using four cases: 90° bend microchannel pressure-driven flow, nanochannel backward facing step with a pressure-driven flow, nanoscale flat plate and NACA 0012 mic...

Numerical Simulation of Turbulent High Speed Plane Jets- a Validation with Experimental Results

Proceeding of Proceedings of the 24th National and 2nd International ISHMT-ASTFE Heat and Mass Transfer Conference (IHMTC-2017), 2018

Mixing streams from flight and exhaust in aerodynamics hold the interest of active flow control a... more Mixing streams from flight and exhaust in aerodynamics hold the interest of active flow control and propulsion studies. This study is aimed at validating an in-house parallel threedimensional solver incorporating the high Reynolds number k-ε model with compressibility correction to check the implementation of the numerical model and its robustness on non homogeneous unstructured grids against experimental dat

Effect of rarefaction on thermal and chemical non-equilibrium for Hypersonic flow with different enthalpy and catalytic wall conditions

Journal of Thermal Science and Engineering Applications

Compressibility and rarefaction effect plays an essential role in the design and study of objects... more Compressibility and rarefaction effect plays an essential role in the design and study of objects experiencing hypersonic flows. The presence of chemical and thermal non-equilibrium in hypersonic flows increases the complexity of estimating aerothermodynamic properties, which are essential for developing thermal protection systems and the aerothermodynamic design of hypersonic vehicles. In this study, the hy2Foam solver, is used to understand the effect of Knudsen number (which in turn depends on the altitude) and free-stream enthalpy variation on the surface aerothermodynamic properties such as pressure, heat flux, velocity slip, temperature jump, and flow-field variables such as species concentration and temperature, in five-species air flow over a cylinder, for both noncatalytic and fully catalytic wall condition. The novelty of the work lies in reporting the effect of rarefaction on thermal and chemical non-equilibrium (associated with hypersonic flows), and thus on the surface ...

Physics of Fluids

The least squares and Green–Gauss gradient schemes have been traditionally studied as two distinc... more The least squares and Green–Gauss gradient schemes have been traditionally studied as two distinct techniques for gradient computation on unstructured meshes in the literature. In this Letter, we show that the Green–Gauss gradient method can be interpreted as a weighted least squares gradient scheme and that methods of the Green–Gauss family may therefore be encompassed in the larger set of least squares-based gradient schemes.

This paper reports a computational and theoretical investigation of pressure-flow characteristics... more This paper reports a computational and theoretical investigation of pressure-flow characteristics of a microchannel having a superhydrophobic bottom wall with embedded air-cavities and, thin deformable membrane as the top wall. Two-way fluid-structure interaction (FSI) and unsteady volume of fluid (VOF) methods are employed for fluid-solid boundary and liquid-air interface at ridge-cavity, respectively. A novel theoretical model has been developed for the pressure-flow characteristics of microchannel with deformable top and superhydrophobic bottom wall. The theoretical and numerical results for pressure drop across the microchannel have shown a good agreement with a maximum deviation of 6.69%. Four distinct types of microchannels viz, smooth (S) (rigid non-textured), smooth with deformable top (SDT), smooth with superhydrophobic bottom (SSB) and, smooth with superhydrophobic bottom and deformable top wall (SSBT) have been investigated for the comparison of their pressure-flow charac...

Evaluation of novel wall function approach for supersonic flow problems involving separations induced by geometry and shocks

Computers & Mathematics with Applications

Investigation of All-Speed SLAU Scheme in Incompressible Limit

Density-based algorithms are generally used to solve high-speed flows; the accuracy of these meth... more Density-based algorithms are generally used to solve high-speed flows; the accuracy of these methods degrades in low-speed limit i.e. in incompressible limit due to a large value of the condition number. A popular method to fix this issue is the use of preconditioning methods. Preconditioning not only maintains the accuracy in low Mach limit but also helps in accelerating the convergence by altering the characteristic speeds, which results in destructions of the time accuracy. Whereas new parameter free scheme has been suggested by Shima which solves the problem without destroying the time-accuracy. In this paper, we investigate the SLAU scheme of Shima in the incompressible limit for practical applications such as aerofoils at an angle of attack using our in-house developed 3-D unstructured hybrid code

A novel least squares finite volume scheme for discontinuous diffusion on unstructured meshes

Computers & Mathematics with Applications, 2021

Application of the K-KL Model to Engineering Flows

Proceeding of Proceedings of the 25th National and 3rd International ISHMT-ASTFE Heat and Mass Transfer Conference (IHMTC-2019), 2019

Computation of Rarefied Gas Flows in Nano/micro Devices using an Indigeneous Developed Computational Fluid Dynamics Solver

Gaseous Nano/micro Electronic Mechanical Systems (NEMS/MEMS) are used for measurement and control... more Gaseous Nano/micro Electronic Mechanical Systems (NEMS/MEMS) are used for measurement and control in the atomic level. Numerical simulation of such system is important for understanding the gas flow behaviour in such devices. Non-equilibrium effects such as small characteristic length, rarefaction and gas-surface interactions characterize such flow behaviour. The Knudsen number, Kn, ratio of the molecular mean free path, λ, to the characteristic length of the geometry, l is used to characterize the translational non-equilibrium of a rarefied gas flow in nano/micro devices. For high gas density with small Kn (Kn≤0.001) the conventional Navier-Stokes (NS) equations are applicable. When the gas density becomes small, the mean free path of gas becomes large and the non-equilibrium effects appear in the flow with fewer collisions between molecules. The conventional NavierStokes equation with velocity slip and temperature jump conditions can be used to simulate the slip-flow regime 0.001≤...

We carry out numerical simulations to optimize the re- entry capsule configurations based on aero... more We carry out numerical simulations to optimize the re- entry capsule configurations based on aero-thermodynamic properties such as drag, pressure and heat load. The open source software OpenFOAM is used with the compress- ible computational fluid dynamics (CFD) solver rhoCen- tralFoam. CFD solver is implemented with the first-order Maxwell’s velocity slip and the Smoluchowski temperature jump boundary conditions. We report results for different altitudes and Mach numbers with varying second cone an- gle and bluntness of the re-entry capsule. It is noted that the heat loads are greatly reduced by changing the capsule con- figuration from single to bi-cone. With increasing second cone angle heat loads are enhanced, but the average drag and pressure coefficients found to be least sensitive. How- ever, with increase in bluntness the average value of heat load decrease slightly and the peak value significantly, while drag values exhibit contrasting behaviour.

Turbulent mixing is highly a ected by uid compressibilty. The current work aims to study the e ec... more Turbulent mixing is highly a ected by uid compressibilty. The current work aims to study the e ect of compressibility corrections for 3 di erent Reynold Averaged Navier Stokes (RANS) turbulence models namely the standard k-epsilon, RNG and Spalart Allmaras models using an in-house parallel three dimensional unstructued CFD solver to compute a high speed mixing layer. The experimental study done by Goebel and Dutton has been used as the benchmark for investigation. The standard kis compared with the RNG model to see the e ect of the change in model coe cients on the predicted ow physics. The one equation Spalart Allmaras model is compared with the aforementioned two equation model to make the performance comparison complete. Turbulent quantities like rate of mixing layer growth, turbulence intensity and normalized Reynold's stress have been compared with benchmark results along with mean ow quantities like the self similar velocity pro les and their results have been presented.

Use of the Pressure Jump Boundary Condition in the High Speed Rarefied Gas Flows

The simulation of rarefied gas flow in hypersonic aerodynamics is important for the design of spa... more The simulation of rarefied gas flow in hypersonic aerodynamics is important for the design of space and re-entry vehicles. Computer simulations can provide the necessary aerodynamic data at less cost and for cases where experiments are difficult to conduct. Therefore, there is a constant effort to develop newer numerical methods and to improve the existing ones based on appropriate physical modeling, so as to make the computer simulations closer to reality. CFD methods are preferred for rarefied flows in the continuum and slip flow regime. The range 0.001 ≤ Kn ≤ 0.01 is called the slip regime, where the no-slip conditions are no longer applicable. The no-slip boundary conditions are replaced in this regime with slip velocity and temperature-jump boundary conditions.

Computational aerothermodynamics is the branch of science which focuses on the computation of the... more Computational aerothermodynamics is the branch of science which focuses on the computation of the effect of thermodynamic and transport models on aerodynamics and heating. They are widely used for external ow cases. On the other hand, the computation of heat and stress in the design of Nano/Micro Electronic Mechanical Systems from the point of view of a Fluid mechanics engineer is also an important area of study. A generalized computational tool which can simulate the low and high speed flows at both the macro and micro levels is desirable from the perspective of industry, academics and research. For a developing nation, it is extremely important to have such a solver developed indigenously to create self-sufficiency and self-reliance. In this work, a robust three-dimensional density-based general purpose computational fluid dynamics solver was developed in house by our research group. The cell centred finite volume discretization method is used on an unstructured grid, which is mor...

Adaptive time-stepping is a method of choosing a variable time-step size for time-marching applic... more Adaptive time-stepping is a method of choosing a variable time-step size for time-marching applications given prescribed tolerance for local error. When applied to steady-state problems this method acts as a convergence accelerator while for transient problems it maintains the time accuracy using a user-prescribed error criterion. In this paper, we demonstrate the usefulness of this method over the commonly-used CFL based time-stepping for different problems with steady/unsteady laminar viscous flow.

Effect of recirculation zone on debris evacuation during EDM deep hole drilling

Procedia CIRP, 2021

International Journal of Numerical Methods for Heat & Fluid Flow, 2020

Purpose The purpose of this study is to present and demonstrate a numerical method for solving ch... more Purpose The purpose of this study is to present and demonstrate a numerical method for solving chemically reacting flows. These are important for energy conversion devices, which rely on chemical reactions as their operational mechanism, with heat generated from the combustion of the fuel, often gases, being converted to work. Design/methodology/approach The numerical study of such flows requires the set of Navier-Stokes equations to be extended to include multiple species and the chemical reactions between them. The numerical method implemented in this study also accounts for changes in the material properties because of temperature variations and the process to handle steep spatial fronts and stiff source terms without incurring any numerical instabilities. An all-speed numerical framework is used through simple low-dissipation advection upwind splitting (SLAU) convective scheme, and it has been extended in a multi-component species framework on the in-house density-based flow sol...

Performance of thek-kLmodel for aerodynamics applications

International Journal of Numerical Methods for Heat & Fluid Flow, 2019

PurposeThe purpose of this paper is to study the predictability of the recently proposed length s... more PurposeThe purpose of this paper is to study the predictability of the recently proposed length scale-based two-equationk-kLmodel for external aerodynamic flows such as those also encountered in the high-lift devices.Design/methodology/approachThe two-equationk-kLmodel solves the transport equations of turbulent kinetic energy (TKE) and the product of TKE and the integral length scale to obtain the effect of turbulence on the mean flow field. In theory, the use of governing equation for length scale (kL) along with the TKE promises applicability in a wide range of applications in both free-shear and wall-bounded flows with eddy-resolving capability.FindingsThe model is implemented in the in-house unstructured grid computational fluid dynamics solver to investigate its performance for airfoils in difficult-to-predict situations, including stalling and separation. The numerical findings show the good capability of the model in handling the complex flow physics in the external aerodyna...

Journal of Turbulence, 2019

Spalart-Allmaras (SA) model is a low Reynolds number (Re) model, which means that the first off-w... more Spalart-Allmaras (SA) model is a low Reynolds number (Re) model, which means that the first off-wall grid point should be placed in the viscous sub-layer with y + 1. This restriction of placing the first off-wall grid point so close to the wall leads to an increase in the mesh size, and thus the computation. The wall function approach is an alternative to this problem. The standard wall function method usually employed has a limitation for cases that involve high adverse pressure gradient and compressibility. This limits its use to the nonseparated flows only. The present work focuses on the formulation of the generalised wall function given by Shih et al. [A generalized wall function; 1999] and applies it to the SA turbulence model, with some modification. The proposed modification was found to remove the oscillation and inaccuracy found in the result when directly using the Shih et al. model. Several flows, with zero pressure gradient to those with adverse pressure gradient leading to flow separation, are solved with the proposed wall treatment, with relatively coarse grids involving y + beyond 50 and up to 100 for certain cases. It is concluded that the results in each case are close to those obtained by the low-Re SA model, despite the use of much coarser meshes.

A Numerical Study of Shock and Heating with Rarefaction for Hypersonic Flow Over a Cylinder

Journal of Heat Transfer, 2019

The numerical computation of hypersonic flows over blunt bodies is challenging due to the difficu... more The numerical computation of hypersonic flows over blunt bodies is challenging due to the difficulty in robust and accurate wall heat flux prediction and proper capturing of shock waves free from the ``carbuncle" phenomenon and other shock anomalies. It is important to understand how these behavior is affected due to rarefaction, which in turn will help to improve the study of aerospace vehicles flowing in rarefied and hypersonic regime. Recently, the SLAU2 convective scheme was shown to suppress the shock anomalies found in capturing strong shocks, however, it still showed a wavy pattern of heating. We have proposed a modification to the SLAU2 convective scheme to improve the accuracy of flow predictions in the presence of strong shocks. We then perform the numerical simulation of hypersonic viscous flow over a cylinder at Mach 888 and 16.3416.3416.34 at different Knudsen numbers. We carry out the study using the modified SLAU2 and the classical Roe schemes. We study how the shock ano...

International Journal of Numerical Methods for Heat & Fluid Flow, 2019

Purpose Accurate prediction of temperature and heat is crucial for the design of various nano/mic... more Purpose Accurate prediction of temperature and heat is crucial for the design of various nano/micro devices in engineering. Recently, investigation has been carried out for calculating the heat flux of gas flow using the concept of sliding friction because of the slip velocity at the surface. The purpose of this study is to exetend the concept of sliding friction for various types of nano/micro flows. Design/methodology/approach A new type of Smoluchowski temperature jump considering the viscous heat generation (sliding friction) has recently been proposed (Le and Vu, 2016b) as an alternative jump condition for the prediction of the surface gas temperature at solid interfaces for high-speed non-equilibrium gas flows. This paper investigated the proposed jump condition for the nano/microflows which has not been done earlier using four cases: 90° bend microchannel pressure-driven flow, nanochannel backward facing step with a pressure-driven flow, nanoscale flat plate and NACA 0012 mic...

Numerical Simulation of Turbulent High Speed Plane Jets- a Validation with Experimental Results

Proceeding of Proceedings of the 24th National and 2nd International ISHMT-ASTFE Heat and Mass Transfer Conference (IHMTC-2017), 2018

Mixing streams from flight and exhaust in aerodynamics hold the interest of active flow control a... more Mixing streams from flight and exhaust in aerodynamics hold the interest of active flow control and propulsion studies. This study is aimed at validating an in-house parallel threedimensional solver incorporating the high Reynolds number k-ε model with compressibility correction to check the implementation of the numerical model and its robustness on non homogeneous unstructured grids against experimental dat