Flow structure and cooling effect of seeping gas film in supersonic turbulent boundary layer

Seeping gas film cooling is an active cooling method that involves injecting a cooling gas film into the boundary layer through porous media. In this study, a sintered wire mesh porous material is used to generate the gas film through seepage flow. The flow of the gas film in the supersonic turbulent boundary layer is observed using nanometer particle plane laser scattering technology, while the temperature distribution of the porous wall surface is measured by infrared thermometry. It is observed that as the injection rate of the gas film exceeds 0.2 %, the supersonic turbulent boundary layer thickens significantly. The rate of thickness growth is promoted from 5.5 % to 17.1 % as the injection rate increases from 0.3 % to 0.8 %. Additionally, the injection of the gas film induces an oblique shock wave, and the shock angle increases with the enhancement of the injection rate, resulting in an uneven cooling effect along the injector length. The transient cooling efficiency of the seeping gas film under thermal non-equilibrium conditions is analyzed. The results indicate that the temperature amplitude on the porous wall surface decreases significantly when the injection rate is promoted from 0.2 % to 0.3 %. However, continuing to increase the coolant injection rate does not lead to a more significant improvement in cooling efficiency. When the injection rate reaches 0.5 %, the relative cooling efficiency reaches 50 % to 60 %, which is much lower than the predicted values of the thin film theory.