Numerical study on mist-assisted film cooling performance under supersonic condition with discrete coolant injection

This study investigates mist-assisted film cooling on a flat plate in a supersonic crossflow (mainstream Ma = 2.0) through numerical simulations under the mist particle diameter of 5 μm. The cooling performance of cylindrical hole, merged hole and sister hole structure is systematically compared at the cooling jet Mach number ranging from 0.4 to 1.4 and mist concentration ranging from 0 to 5%. The effects of shock system, kidney vortex pair and mist particles distribution on film cooling performance are analyzed. Results demonstrate that increasing the cooling jet Mach number could intensify the shear layer effect, shock waves interaction and kidney vortices, promoting both the jet lift-off and mist particle lift-off phenomena, thus reducing the cooling performance enhancement obtained by the mists injection at the near-hole region. Increasing the mist concentration could primarily improve the cooling performance at the more downstream region where the cooling capacities of the air jets decay rapidly and more mist particles diffuse onto the wall surface. Results also indicate that proper management of vortex structures and expansion wave impingement location enable more effective mist transport to protect the wall surface. Among three configurations, sister holes demonstrate superior overall cooling performance in both air-only and mist-assisted conditions, particularly at a higher jet Mach number. Under Mac = 1.4 and 5% mist concentration, sister holes achieve a 40% enhancement and merged holes achieve a 16% enhancement in cooling effectiveness compared to cylindrical holes.