Numerical investigation on the double-layer porous plate of transpiration cooling with phase change under different heat flux

Abstract

Transpiration cooling is a potential active thermal protection method for aircraft under severe thermal environment. Though it is cooling efficiency that is of concern in most structural designs, the injection pressure is equally critical for transpiration cooling especially when using liquid as coolant. To enhance the cooling performance of transpiration cooling with phase change, double-layer porous plate that upper and lower layers have different porosities is presented and adopted. A new numerical simulation model, modified Two-Phase Mixture Model with Local Thermal Non-Equilibrium is used to investigate two-phase flow and fluid-solid coupled heat transfer under different heat flux. The results reveal that overall pressure drop of the porous plate is mostly dependent on vapor region which has higher flow resistance, so designing larger porosity for the upper layer where is occupied by vapor region can effectively reduce the coolant injection pressure. Besides, since the specific heat of liquid is larger than that of vapor, designing smaller porosity for the lower layer where liquid region is located can lead to lower surface temperature when increasing coolant mass flow. Moreover, designing a thinner lower layer in the region exposed to high heat flux could obtain desired coolant distribution. The double-layer porous plate with unequal thickness can reduce the injection pressure by 20.8 % and improve its relative uniformity by 33.3 % while decreasing the surface temperature at the same time. The new evaluation of cooling performance and the new structure have important guidance and practical significance of transpiration cooling in the actual application of aircraft in severe thermal environment.

Keywords

• Transpiration cooling
• Water phase change
• Porous medium
• Thermal protection