Effects of wall thermal state on the cooling and friction reduction characters for supersonic film using gaseous hydrocarbon fuel

Film cooling using gaseous hydrocarbon fuel is an effective way to meet the thermal protection and friction reduction demands of hydrocarbon-fueled scramjet engines. The cooling and friction reduction characteristics of the hydrocarbon film can be influenced by the wall thermal state through the variation of endothermic and exothermic chemical reactions in the film. Numerical investigations based on the RANS method have been performed to evaluate the effects of the wall thermal state on the hydrocarbon slot film cooling performance. Four wall thermal states which represent different regenerative cooling levels are simulated. Results show that an increase of the wall cooling heat flux is beneficial to the film cooling performance while has unfavorable effects on the film friction reduction performance. Further analysis reveals that the net energy effects of the chemistry in the hydrocarbon film can be equivalent to an additional constant wall cooling heat flux of -0.36 MW/m(2) within a certain range. Besides, the proportion of this equivalent wall cooling heat flux in the total wall cooling heat flux decreases from 100% to 26% for different wall thermal states. Therefore, the cooling enhancement brought by the endothermic chemistry is comparable to the regenerative cooling. However, the wall shear stress is less sensitive to the wall thermal state. The maximum deviation of the total wall friction for different wall thermal states is less than 8% compared to the reference value.