Large eddy simulation of film cooling with different upstream obstacles

Large eddy simulations (LES) of jet in crossflow (JICF) by modifying the upstream obstacles for enhancing the film cooling performance are performed in this study. Three types of upstream obstacles are considered, i.e. no obstacle, step and ramp placed upstream of the film cooling orifice. The numerical methods and mesh resolution are carefully validated with the experimental data. The predicted results show that the designed upstream obstacle leads to the changes of the flow structure and has a great improvement on the adiabatic cooling efficiency. The obstacle affects the development of the boundary layer upstream of cooling jet orifice and the recirculation zones are formed between the upstream obstacle and cooling jet orifice. The formation of horseshoe vortex structures are suppressed by the formed recirculation zones, which indicates that the existence of the recirculation zone enables some cooling gas to enter the recirculation zone and increases the air film cooling effects in the near field, which is conducive to the improvement of adiabatic cooling efficiency. The case with ramp has the best overall film cooling performance among the configurations considered in this work, especially on the wall surface away from the central plane. Besides, the cooling efficiency and characteristics with different upstream obstacles have also been addressed.