Numerical investigation on thermal insulation effect by coolant layer in performance of transpiration cooling

The principle of transpiration cooling involves the internal convective heat transfer within the porous medium and the external thermal insulation by the coolant layer. This work quantitatively analyzed the insulation effect to deeply understand the mechanism of transpiration cooling. The average heat absorption power ratio is 1.12 under the 0.8 % injection ratio, indicating a greater contribution of thermal insulation to the performance of transpiration cooling. An increase in the injection ratio enhances the thermal insulation effect at the end of the porous medium, and the maximum heat absorption power ratio reaches 3.65 at the injection ratio of 0.9 %. Although a change in the mainstream Mach number leads to an overall alteration in the heat absorption power of both aspects, the average heat absorption power ratio of thermal insulation to convective heat transfer improves as the Mach number rises. The thermal insulation effect weakens with an increase in shock wave intensity. An exponential functional relationship exists between the average thermal insulation effect and the wedge angle. Under a wedge angle of 12°, the contribution of thermal insulation is less than that of the convective heat transfer in the porous medium, and the heat absorption power ratio drops to 0.52.