Modeling and simulations of variable-density flows

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 meaningfully 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 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 can 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.

About the speaker

Dr. Sidharth GS is an assistant professor in the Deptartment of Aerospace Engineering at Iowa State University. He was previously a postdoctoral researcher at the Los Alamos National Laboratory, where he worked on modeling mix and burn in multimaterial turbulence and separately on feature based dynamic reconstructions. He received his PhD at the University of Minnesota, specializing in computations of hypersonic flows and modeling variable-density subgrid effects relevant to supersonic combustion.