Mixing and turbulent kinetic energy scaling in compressible reacting flows

Previous work by these authors analyzed in depth vorticity generation and transport in supersonic flows in order to understand the physics of supersonic combustion and to improve air-hydrogen mixing. In fact, the short combustor residence time (10-3- 10-4 s) minimizes the chance to completely mix and burn the fuel. Thus it becomes imperative to create there very energetic vortex structures, and a solution is to inject hydrogen in crossflow. In this paper, the 3D LES of the supersonic combustor flight tested in the HyShot project showed that the interactions between the airstream entering the combustor and the H2 sonic jet produce average vorticity of order 105 Hz, with much higher localized peaks. The interaction between the hydrogen jets and the supersonic airflow leads to a bow shock formation in front of each jet and boundary layer separation. This separation allows H2 to be convected upstream through spanwise vortices created by the baroclinic effect. Once created, vortices are tilted, stretched, compressed and expanded as predicted by the fully compressible vorticity transport equation. This paper is meant to expand and complement earlier works showing how vortices affect combustion and analyzing the main species distribution along the combustor. The spectral analysis of turbulent kinetic energy obtained by LES results demonstrates that where compressibility is not negligible, the turbulent kinetic scaling differs from Kolmogorov. © 2011 by Antonella Ingenito & Claudio Bruno.