Abstract
Large eddy simulations (LESs) on the well-known 7-7-7 fan shaped cooling hole were carried out. Like using a trip strip to create turbulent boundary layer in practical experiments, trip strips with different configurations were placed upstream of the cooling hole to investigate incoming turbulent boundary layer effect on the film cooling flow behavior. Without the trip, horseshoe vortex generated by laminar boundary layer induced laterally discharging cooling flow in the lateral direction. Meanwhile, the induced cooling flow formed high film cooling effectiveness region around the film cooling hole. When the incoming boundary flow was turbulent, laterally discharged cooling flow was influenced by the turbulent boundary layer to dissipate to the main flow and resultant high effectiveness region disappeared. Depending on the trip configuration, quantitative characteristics of boundary layer such as turbulent intensity, momentum thickness, and shape factor were strongly affected. Some trip configurations resulted in fully developed turbulent boundary layer just before leading edge of the film cooling hole. In such cases, distribution of the film cooling effectiveness showed a reasonable agreement with available experimental data where the quantitative properties of the turbulent boundary layer were similar. However, when the trip was located too close to the film cooling hole, the separated and reattached flow did not develop into the stabilized turbulent boundary layer. Then strong turbulence intensity in the main flow boundary layer stimulated break down of the cooling flow vortex structure and early dissipation to the main flow. It resulted in restricted film cooling flow coverage.
