Enhanced turbine endwall cooling using crescent-dimpled film cooling holes and a hybrid configuration: numerical study

The current study proposed a novel crescent-dimpled film cooling hole and investigated its aerothermal performance on the turbine endwall when a row of the film holes are arranged in front of the stator. The mainstream Reynolds number based on the inlet velocity and the axial chord length of the vane was 150,000, and the blowing ratio ranged from 0.5 to 1.5. Besides, a hybrid configuration combining the advantages of the cylindrical and crescent-dimpled holes was also investigated. RANS simulations using Shear Stress Transport (SST) k - omega turbulence model were conducted. The numerical simulations show that the pure crescent-dimpled hole design enhances the adiabatic film cooling effectiveness by 32.3 %, 52.3 %, and 43.6 % at blowing ratios of 0.5, 1.0, and 1.5, respectively. Correspondingly, the net heat flux reduction (NHFR) values are 22.9 %, 57.9 %, and 63 % higher than the cylindrical holes. The high film cooling effectiveness behind the film cooling hole prevents the additional thermal load caused by the dimple-induced heat transfer enhancement. Using cylindrical holes near the leading edge and crescent-dimpled holes elsewhere, the hybrid arrangement suppresses the passage vortex and further enhances the film cooling effectiveness and NHFR by 51.9 % and 93.8 % at BR = 1.5, respectively. The streamlines and vortex structures show that the crescent dimple at the hole's exit diffuses the coolant, thereby enhancing the film cooling in the lateral direction. Flow separation occurs behind the dimple, which reduces the jet momentum and attracts the jet towards the wall. The curved surface of the dimple directs the horseshoe vortex in front of the jet to the side, and anti-CRVP is formed. These are responsible for the film cooling enhancement by the crescent dimple.