MAE Seminar – Theory, Modeling, and Simulations of Variable-Density Flows

Department of Mechanical and Aerospace Engineering

THEORY, MODELING, AND SIMULATIONS OF VARIABLE-DENSITY FLOWS

Sidharth GS, PH.D.

Postdoctoral Research Scientist, Los Alamos National Laboratory

Abstract:  Density variations on the order of mean density are encountered in many technological and natural flows. These variations arise from compressibility, heat transfer, compositional inhomogeneity and/or reactions. Baroclinic torque, from misaligned density and pressure gradients is an important vorticity production mechanism. (1) To explicitly represent baroclinic and dilatation effects on turbulent dissipation, we derive a new form of the governing equations for large eddy simulations, which drastically simplifies the closure problem as it involves only double correlations, and not triple and higher correlations that appear in the conventional equations. We demonstrate the use of the new equations in complex flows. (2) Non-local linear instabilities play a central role in transition to turbulence in hypersonic boundary layers. Using global tools, we analyze such instabilities in separation zones and identify the role of centrifugal and baroclinic effects in the transition mechanism. (3) Diffusive models with an eddy viscosity are the norm in engineering turbulence closures. However, strong anisotropy and counter-gradient effects require that simulations represent the turbulent processes more accurately. We discuss these aspects in the context of scalar transport by turbulence. All these topics account to put engineering simulations of high-speed aerodynamics and propulsion on a first principles basis.

Dr. Sidharth GS is a postdoctoral researcher at the Los Alamos National Laboratory, where he works on multimaterial turbulence and physics-informed dynamic reconstructions. He received his PhD at the University of Minnesota specializing in computations of hypersonic flows.