This study introduces the creation of straightforward and reliable algorithms aimed at simulating... more This study introduces the creation of straightforward and reliable algorithms aimed at simulating compressible Euler equations featuring a stiffened gas equation of state (EOS). These algorithms are crafted to faithfully depict gaseous mixtures in thermal equilibrium, excluding chemical reactions. The methodology relies on a fully conservative approach within a finite volume framework, employing central schemes with controlled numerical diffusion. The RICCA and MOVERS+ algorithms implement two models, specifically Mass fraction (Y) and Mixture gamma (γ) based models. These models adeptly capture the fundamental characteristics of flow fields. Rigorous testing of the numerical schemes ensures the minimization of pressure oscillations and the preservation of mass fraction positivity, especially in first-order numerical methods. A series of one-dimensional (1D) and two-dimensional (2D) test cases are presented to showcase the effectiveness and precision of the developed algorithms. These tests provide compelling evidence of the algorithms' resilience and accuracy in simulating the intended flow phenomena.
Aerodynamic shape optimization problems often have multi-modal and multi-objective cost functions... more Aerodynamic shape optimization problems often have multi-modal and multi-objective cost functions and a high computational expense associated with calculating them. Hybrid optimization algorithms comprised of non-gradient and gradient-based optimization procedures help obtain global minima and reduce computational cost. This paper proposes a hybridization strategy that takes advantage of the clustering of particles to switch to a gradient-based approach and obtain multiple optima. No information on the modality of objective function needs to be known, thus making it suitable for applications like aerodynamic optimization. Reduced costs have, and accurate convergence to multiple optimal solutions has been shown for several test functions. The procedure was also applied to the design of a two-dimensional hypersonic inlet, optimizing the pressure recovery.
Non-classical non-linear waves exist in dense gases for large specific heats at pressures and tem... more Non-classical non-linear waves exist in dense gases for large specific heats at pressures and temperatures of the order of critical point values. These waves behave precisely opposite to the classical non-linear waves, with inverted classical waves like the expansion shocks which do not violate entropy conditions. More complex equation of state (EOS) other than the ideal or perfect EOS is typically used in describing dense gases. Algorithm development with non-ideal/real gas EOS and application to dense gasses is gaining importance from a numerical perspective. Extending the algorithms designed for perfect gas EOS to dense gas flows with arbitrary real gas EOS is non-trivial. Most of the algorithms designed for prefect gas EOS are modified significantly when applied to real gas EOS. These algorithms can become complicated and some times impossible based on the EOS under consideration. The objective of the present work is to develop central solvers with smart diffusion capabilities i...
Scramjet inlet design remains as a key aspect for hypersonic flight. To assess the inlet design, ... more Scramjet inlet design remains as a key aspect for hypersonic flight. To assess the inlet design, the performance parameters namely; aircapture ratio, total pressure efficiency, inlet drag coefficient, and kinetic energy efficiency are evaluated and analysed. In the current study comparison of performance parameters is carried out by performing numerical computation of 2-D turbulent flow field for four different scramjet inlet geometries with two different free stream Mach number (M=4 and 5). The numerical computation is performed with the help of Femlab’s finite element method tool “Comsol Multiphysics” using the “Turbulent High Mach Number Flow” module provided in it.
Numerical study of aerodynamic characteristics in steady laminar supersonic flow over a double we... more Numerical study of aerodynamic characteristics in steady laminar supersonic flow over a double wedge airfoil is carried out using commercially available finite element based CFD tool COMSOL Multiphysics. The aerodynamic characteristics of double wedge airfoil like lift and drag are analyzed by solving Navier-Stokes equations in the flow field for various thickness to chord ratios (t_c) and angle of attack α at free stream Mach number M=2.5. In the present work the high Mach number flow module with pseudo time stepping methodology and adaptive gridding technique is used to obtain a steady state solution by marching in time and to capture the shocks occurring in the flow field. The simulation were performed for 21 cases and for each case the Euler solution was first obtained and then was made as the initial condition for viscous simulation. The aerodynamic coefficients such as CL, CD and CP are evaluated from both shock expansion theory and numerical simulation of Navier-Stokes for do...
Simple and robust algorithms are developed for compressible Euler equations with stiffened gas eq... more Simple and robust algorithms are developed for compressible Euler equations with stiffened gas equation of state (EOS), representing gaseous mixtures in thermal equilibrium and without chemical reactions. These algorithms use fully conservative approach in finite volume frame work for approximating the governing equations. Also these algorithms used central schemes with controlled numerical diffusion for this purpose. Both Mass fraction (Y ) and based models are used with RICCA and MOVERS+ algorithms to resolve the basic features of the flow fields. These numerical schemes are tested thoroughly for pressure oscillations and preservation of the positivity of mass fraction at least in the first order numerical methods. Several test cases in both 1D and 2D are presented to demonstrate the robustness and accuracy of the numerical schemes.
Heavy-duty motors are used in marine applications for supplying cooling water to internal combust... more Heavy-duty motors are used in marine applications for supplying cooling water to internal combustion engines, seawater to ballast tanks, and for sewage operations. Cooling of these heavy-duty electric motors is an important issue concerning the performance of the motor. Heat is dissipated from the motor surface via conduction, convection and radiation. For enhancing heat transfer rate, fins are provided thereby increasing the effective area of cooling. Owing to the space constraints in marine applications a cooling fan is mounted integral to the motor shaft to facilitate the motor with forced convection cooling. In this work, suitability of mixed flow fan for heavy-duty motors is studied using CFD for flow optimization. The results of CFD are used for prediction of the radiated noise. The CFD code prediction of noise levels is found to meet design criteria of 70dB.
The nonlinear convection terms in the governing equations of compressible fluid flows are hyperbo... more The nonlinear convection terms in the governing equations of compressible fluid flows are hyperbolic in nature and are nontrivial for modelling and numerical simulation. Many numerical methods have been developed in the last few decades for this purpose and are typically based on Riemann solvers, which are strongly dependent on the underlying eigen-structure of the governing equations. Objective of the present work is to develop simple algorithms which are not dependent on the eigen-structure and yet can tackle easily the hyperbolic parts. Central schemes with smart diffusion mechanisms are apt for this purpose. For fixing the numerical diffusion, the basic ideas of satisfying the Rankine-Hugoniot (RH) conditions along with generalized Riemann invariants are proposed. Two such interesting algorithms are presented, which capture grid-aligned steady contact discontinuities exactly and yet have sufficient numerical diffusion to avoid numerical shock instabilities. Both the algorithms p...
Heavy-duty motors are used in marine applications for supplying cooling water to internal combust... more Heavy-duty motors are used in marine applications for supplying cooling water to internal combustion engines, seawater to ballast tanks, and for sewage operations. Cooling of these heavy-duty electric motors is an important issue concerning the performance of the motor. Heat is dissipated from the motor surface via conduction, convection and radiation. For enhancing heat transfer rate, fins are provided thereby increasing the effective area of cooling. Owing to the space constraints in marine applications a cooling fan is mounted integral to the motor shaft to facilitate the motor with forced convection cooling. In this work, suitability of mixed flow fan for heavy-duty motors is studied using CFD for flow optimization. The results of CFD are used for prediction of the radiated noise. The CFD code prediction of noise levels is found to meet design criteria of 70dB.
Non-classical non-linear waves exist in dense gases at high pressure in the region close to a the... more Non-classical non-linear waves exist in dense gases at high pressure in the region close to a thermodynamical critical point. These waves behave precisely opposite to the classical non-linear waves (shocks and expansion fans) and do not violate entropy conditions. More complex EOS other than the ideal or perfect gas equation of state (EOS) is used in describing dense gases. Algorithm development with non-ideal/real gas EOS and application to dense gasses is gaining importance from a numerical perspective. Algorithms designed for perfect gas EOS can not be extended directly to arbitrary real gas EOS with known EOS formulation. Most of the algorithms designed with prefect gas EOS are modified significantly when applied to real gas EOS with the known formulation. These algorithms can become complicated and some times impossible based on the EOS under consideration. The objective of the present work is to develop central solvers with smart diffusion capabilities independent of the eigen...
Non-classical non-linear waves exist in dense gases at high pressure in the region close to a the... more Non-classical non-linear waves exist in dense gases at high pressure in the region close to a thermodynamical critical point. These waves behave precisely opposite to the classical non-linear waves (shocks and expansion fans) and do not violate entropy conditions. More complex EOS other than the ideal or perfect gas equation of state (EOS) is used in describing dense gases. Algorithm development with non-ideal/real gas EOS and application to dense gasses is gaining importance from a numerical perspective. Algorithms designed for perfect gas EOS can not be extended directly to arbitrary real gas EOS with known EOS formulation. Most of the algorithms designed with prefect gas EOS are modified significantly when applied to real gas EOS with the known formulation. These algorithms can become complicated and some times impossible based on the EOS under consideration. The objective of the present work is to develop central solvers with smart diffusion capabilities independent of the eigen...
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Papers by Ramesh Kolluru