Large eddy simulation is performed to study the thermal energy transport and mixing process of a round laminar jet in a fully-turbulent high-Mach-number crossflow. In this study, the energy equation of highly compressible fluid is systematically analyzed and the contributions of each term in the equation are compared quantitatively. Turbulent enthalpy transport is found to be in the same order of magnitude as the advection term associated with mean motion and thus is not negligible when considering the convective heat transfer problem of film cooling, which differs from the conclusion drawn from the incompressible-jets-in-crossflow studies. The inaccuracy of RANS turbulent modeling caused by counter-gradient transport of enthalpy is explained in detail and a more reasonable three-dimensional analysis method is proposed for in-depth mechanism analysis and turbulent model improvement. The numerical results also show that the contribution of mean motion to the overall kinetic energy dissipation in thermal energy transport is dominant in the near-field region where jets and crossflow interact and mix intensively while the turbulent kinetic energy dissipation term predominates in most other regions. Moreover, the irreversible increase in entropy caused by dissipation and heat transfer in the flow field is compared. The results show that the entropy production due to the latter one cannot be ignored when dealing with large temperature difference film cooling which is common in high-pressure turbines.

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