Experimental investigation of seeping gas film cooling effect at downstream wall in hypersonic flow

Generating a seeping gas film through porous material to cover the downstream wall can achieve a large-area thermal protection from aerodynamic heating for the windward surfaces of hypersonic vehicles. This study explores the cooling efficiency of the seeping gas film downstream of the porous wall through experimental research. It introduces a continuous high-temperature wind tunnel heat flux calculation method and investigates the influence of cooling gas injection rate and blowing length on downstream wall cooling efficiency. Additionally, an engineering evaluation of the thermal protection effect of the seeping gas film on the downstream wall of the flat plate boundary layer is conducted. Experimental findings demonstrate that cooling efficiency decreases rapidly along the flow direction, and an increase in the cooling gas injection rate enhances the cooling efficiency downstream of the porous wall, while the attenuation rate of cooling efficiency in the downstream region accelerates with higher injection rates. Moreover, a rise in injection rate results in a reduction of the effectiveness-cost ratio in the upstream region, with the seeping gas film's effectiveness-cost ratio being relatively high at an injection rate of 0.2 %. Longer blowing lengths enhance the cooling efficiency at the end of the porous wall but accelerate the attenuation rate of cooling efficiency along the flow direction. Conversely, under constant blowing length, a higher injection rate contributes to a faster attenuation rate of cooling efficiency downstream. Assessment of the thermal protection effect for different combinations of blowing lengths (20 similar to 60 mm) and injection rates (0.1 %similar to 0.5 %) reveals that layouts featuring shorter blowing lengths and higher injection rates demonstrate superior cooling effects downstream of the porous wall when supplied with the same mass flow rate.