A novel numerical coupling strategy for hypersonic transpiration cooling: Instantaneous local phase change at the high-enthalpy porous interface

Transpiration cooling with phase change has been acknowledged as one of effective thermal protection systems (TPS) for hypersonic flight. To enhance TPS reliability, uncovering the complex coupled interaction between the internal porous media flow and the external high speed free flow is of great importance. In order to overcome such issue, this paper has established an improved interfacial coupling strategy based on numerical simulation method, to enhance the accuracy of predicting the transpiration cooling performance of a blunt body in hypersonic flow with coolant of liquid water considering phase change. Leveraging the instantaneous local phase change theory under the high-enthalpy condition, the implementation of this new coupling strategy considering both heat and mass transfer at the transpiration interface improves from three aspects, which are the thermal expansion with velocity variation during phase change from liquid to gas phase, latent heat of vaporization, and thermal gradient variations in the boundary layer, respectively. A careful validity of the proposed interfacial coupling strategy is firstly conducted by comparing with the experimental result at Ma 4.2. The results show that the proposed interfacial coupling strategy holds a maximum 1.3 % error of the cooling efficiency at the stagnation region, significantly improving the prediction accuracy compared with the traditional numerical coupling simulation method. Moreover, the effect of porous media porosity and covering ratio on transpiration cooling performance are investigated under various conditions of coolant mass flux and freestream Mach number. The results imply a critical threshold of water coolant mass flux, exceeding which the transpiration cooling efficiency shows limited improvement. This work offers a superior interfacial coupling method for transpiration cooling applications of TPS, as well as providing a useful numerical tool to predict and improve the cooling efficiency.