Direct Numerical Simulation of Foreign-Gas Film Cooling in Supersonic Boundary-Layer Flow

The cooling-film behavior in an adiabatic supersonic air main flow over a flat plate is investigated using direct numerical simulations. Air and helium are employed as cooling gases and are injected with a low rate in the wall-normal direction through a single infinite spanwise slit into the laminar or turbulent boundary-layer flow. The blowing is realized by prescribing a fixed distribution of the cooling-gas mass flux, mass fraction, and temperature at either the orifice location without the cooling-gas channel (modeled blowing) or at the lower end of the included blowing channel (simulated/interacting blowing), thus allowing for an interaction of the main and cooling-gas flows. The influence of the modeling, the main-flow boundary-layer state, and the cooling-gas type on the film-cooling effectiveness and the skin-friction alteration is scrutinized; and valuable data for the validation of less costly computational fluid dynamics methods employing turbulence models are gained from this fundamental study.