Large eddy simulation of highly compressible film cooling in transonic crossflow

Abstract

Large eddy simulation is performed to study the thermal energy transport and mixing process of compressible film cooling in the fully-turbulent high-Mach-number crossflow. Three Mach numbers, 0.8, 1.2, and 1.4, based on the bulk crossflow velocity, are adopted. And the influence of both the compressibility and shock waves on the transverse jet from cylindrical orifices is discussed in detail. The results reveal that the effects of compressibility should be distinguished from shocks in supersonic flows. The compressibility effect strengthens the jet penetration and lateral spreading by increasing the energy contained in the large-scale coherent structures. The mixing of the jet is enhanced by the strong compressibility in the near field whether shocks exist or not. When the crossflow transits from the subsonic to the supersonic state, the effect of shock waves becomes more significant than that of the compressibility. Various interactions between shocks, coherent structures, and thermal energy transport are analyzed in this study. The results show that the appearance of the separation shock and bow shock reduces the jet penetration and strengthens its interaction with the bottom wall. The generation of this type of shock system suppresses the flow separation on the leeward side of the jet, which results in a higher cooling effectiveness in the jet near field. The incident oblique shock wave also induces lifting of the jet trajectory in the far-field region as a result of the intensified separation trend. In the highly compressible film cooling process with great temperature difference, the advection transport associated with turbulent motion, rather than the one associated with mean motion, turns out to dominate the thermal energy transfer in general. Moreover, the counter gradient behavior of this thermal energy transport in compressible turbulence is also shown.