Large Eddy Simulations on Fan Shaped Film Cooling Hole With Various Inlet Turbulence Generation Methods

Large eddy simulations on well-known 7-7-7 fan shaped cooling hole have been carried out. Film cooling methods are generally applied to high pressure turbine, of which flow condition is extremely turbulent because high pressure turbines are generally located downstream combustor in gas turbines. However, different to RANS simulations, implementing turbulence at the main flow inlet is not simple in LES. For this reason, several numerical techniques have been devised to give turbulence information at the inlet boundary condition in LES. In this study, rectangular turbulator was located in front of the cooling hole to generate turbulent boundary flow in the main flow. Another method used in this study is transient table method to simulate turbulent flow at the main flow inlet. Without turbulent velocity components in approaching flow, laterally discharged cooling flow touches wall while it forms a vortex structure. Then high film cooling effectiveness region around the cooling hole appears. In the meanwhile, when approaching flow is turbulent, the laterally discharged cooling flow no more forms vortex structure and dissipated to the main flow and resultant high effectiveness region disappears. Both turbulence generation methods showed that turbulent intensity of the main flow affects effective range of the cooling flow and resultant film cooling effectiveness distributions. Also high turbulence intensity of the main flow stimulates early break down of the vortex structure coming out of the cooling hole and its dissipation to the main flow. It means high turbulent intensity restricts film cooling flow coverage. Another lesson from the study is that vortex generated from the cooling hole, its development and dissipation to the main flow, have an important role to understand film cooling effectiveness distributions around the cooling hole.