Multi-scale investigation of cooling characteristics and structural arrangement effects in octahedral transpiration cooling structures

The internal heat transfer mechanism of periodically arranged transpiration cooling structures remains unclear. In this study, the differences in simulation results between the pore-scale method and volume-averaged method are firstly compared. After determining the appropriate simulation method, the film outflow characteristics and film coverage performance of single octahedral concave film holes are revealed from the perspective of film formation mechanism. On the basis of clarifying the internal cooling mechanism of unit cells, the overall flow and heat transfer characteristics as well as their variation trends of regularly arranged octahedral transpiration cooling structures are analyzed in terms of streamwise arrangement and layer height layout. The results show that the volume-averaged method produces an error of 28.56% compared with the pore-scale method, which fails to accurately simulate transpiration structures with complex flow disturbance elements. Three typical outflow states exist in the concave film holes of octahedral transpiration structures, which can be distinguished by the coolant momentum density at the inlet surface of 2.13 kg/(m 2 ·s) and 3.89 kg/(m 2 ·s). Increasing the number of unit cells along the mainstream direction weakens the overall cooling performance of the front and middle structural regions. Raising the layer number improves film coverage and enlarges heat transfer area, yet it also causes a sharp rise in pressure drop. With comprehensive performance taken into consideration, the double-layer octahedral transpiration cooling structure achieves the optimal overall cooling effect.