Direct Numerical Simulation of Supersonic Film Cooling Enhanced by a Backward-Facing Step

Supersonic film cooling is an effective strategy for thermal protection of hypersonic vehicles. The present study proposes a modified supersonic film-cooling configuration by introducing a backward-facing step beneath the film slot. Direct numerical simulations are conducted to investigate the flow characteristics and cooling performance across different step heights. The results show that the introduction of the step enhances film-cooling performance, and this effect becomes more pronounced as the step height increases. Within the investigated range, a maximum improvement of 45% is achieved as compared with the baseline case without a step. The step delays the mixing between the film and the mainstream, thereby extending the film coverage length. Further analysis of wall heat flux decomposition reveals that the extension of the effective cooling length is primarily caused by a reduction in the contribution from viscous dissipation. This reduction results from both the decreased shear stress beneath the film caused by the recirculation region and the suppression of turbulence development. Although the step enhances film-cooling performance, it also induces an aerodynamic penalty due to increased pressure drag. The optimal tradeoff between cooling enhancement and aerodynamic loss is achieved when the step height is equal to the film slot height.