Numerical Investigation and Optimization of Transpiration Cooling Plate Structures with Combined Particle Diameter

Transpiration cooling is an efficient thermal protection technology used for scramjet combustors and other components. However, a conventional transpiration cooling plate structure with uniform porous media distribution suffers from a large temperature difference between the upstream and downstream surfaces and high coolant injection pressure (p). To enhance the overall cooling effect and reduce the maximum surface temperature and coolant injection pressure, the combined particle diameter plate structure (CPD−PS) is proposed. Numerical simulations show that compared with the single-particle diameter plate structure (SPD−PS), the CPD−PS with a larger upstream particle diameter (dp) than that of the downstream (dpA > dpB) can effectively reduce the upstream temperature and improve average cooling efficiency (ηave). Meanwhile, gradually increasing dp will increase the permeability of porous media, reduce coolant flow resistance, and thus lower coolant injection pressure. An optimization analysis of CPD−PS is conducted using response surface methodology (RSM), and the influence of design variables on the objective function (ηave and p) is analyzed. Further optimization with the multi-objective genetic algorithm (MOGA) determines the optimal structural parameters. The results suggest that porosity (ε) and dp are the most crucial parameters affecting ηave and p of CPD−PS. After optimization, the maximum temperature of the porous plate is significantly reduced by 8.40%, and the average temperature of the hot end surface is also reduced. The overall cooling performance is effectively improved, ηave is increased by 6.02%, and p is significantly reduced. Additionally, the upstream surface velocity of the optimized structure changes and the boundary layer thickens, which enhances the thermal insulation effect.