Shock/Boundary Layer/Heat Release Interaction inthe HyShot II Scramjet Combustor

Previous computational work by these authors showed a very complex structure arising within the HyShot II combustor due to the interaction between the sonic crossflow injection and the airstream flowing at M =2.78. In that work, a 3D Large Eddy Simulation (LES) of the HyShot II combustor was performed with a 14*106 nodes structured grid. In the present work, in order to analyze in higher details the structures occurring within the HyShot II combustor, a fairly refined grid of 52*106 nodes has been adopted. The LES simulations have been performed by means of a in-house code (S-HeaRT, Supersonic Heat Release and Turbulence): here, the LES model is based on a high order with lowdiffusion numerical schemes to accurately reproduce complex shock interactions, contact surfaces without artificially damping resolvable scales of turbulence. A hybrid method has been implemented to properly capture shocks while at the same time solving the transport equations away from discontinuities via a low dissipation, central scheme with fourth order accuracy. Simulations performed by means of the fairly accurated grid predicts very complex 3D flow structures arising within the flowfleld due to the blockage induced by the H2 transverse injection. Ahead of each H2 injector a bow shock forms: the interaction of the bow shock and the boundary layer leads to a boundary layer separation zone where recirculation of H2 is allowed. In this recirculation zone, the presence of OH radical is predicted by LES indicating that a flame starts already in the injectors upstream the recirculation zone, downstream the flow separation. LES predicts the formation of barrel shock due to the H2 expansion: here the H2 jet expands untill it is definitively recompressed through the Mach disc. These flow structures, such us the bow and the barrel shocks, the Mach disk, the jet vortices and the horseshow vortices are in very good agreement with experimental results. Interactions among the airstream entering the combustor, the heat released and the shock waves produce a large vorticity rate that enhances and accelerates turbulent mixing. The vortex shedding, merging and tilting has also been analyzed, pointing out the contribution of the baroclinic term to the vortex generation and intensification. LES predicts a very fast and efficient combustion: only 0.5% of hydrogen is found unburned at the combustor exit. Comparison of pressures distribution along the wall centerline at 1.2 ms shows a good agreement, mostly in the first part of combustor, where the grid is much more refined.