Favorable-Pressure-Gradient Influence on Supersonic Film Cooling with Turbulent Main Flow

Cooling of a hot supersonic turbulent boundary-layer flow by wall-parallel blowing of a high-heat-capacity gas through a backward-facing step is an effective method to protect the wall from heat overload. Detailed fundamental investigations in previous work concentrated on the flat-plate film-cooling case with zero streamwise pressure gradient (ZPG). In the application to the nozzle-extension wall of a rocket engine however the pressure decreases significantly, accelerating the flow, and it needs be known whether this has a significant effect on the mixing and heat-transport processes. To this end, a fundamental direct-numerical-simulation study has been performed using largely the same setup as in the ZPG case to elucidate the influence of a ‘favorable’ pressure gradient on the cooling and mixing region for a superheated-steam flow with initial Mach number 3.3, cooled by helium injection with Mach 1.8.