Scale-based energy transfer mechanisms in supersonic combustion

Many turbulence closure models for Large Eddy Simulation (LES) are based on the concept of the turbulence energy cascade in which the turbulence energy is described as being transferred in an inviscid manner from large scales to progressively smaller and smaller scales until it is dissipated at the Kolmogorov length scales. The validity of this assumption of net-downward energy transfer across the LES filter scale is uncertain in the regime of compressible reacting turbulence. In this work, we investigate the phenomena of scale-dependent turbulent kinetic energy backscatter in the DNS of both non-reacting and reacting spatially developing shear layers with the goal of understanding how the energy cascade is altered in the presence of strong shocks and heat release. A configuration in which an incident shock impinges on the shear layer is also considered. Results show that at certain filter-to-grid ratios, significant amounts of local backscatter do occur. Correlations between the backscatter and other flow phenomena, such as heat release, pressure dilatation, and vorticity, will be reported. Cross-scale transport of reacting species scalar variance is also investigated.