Discharge coefficients and aerodynamic losses for cylindrical and cratered film-cooling holes with various coolant crossflow orientations

Abstract

In addition to cooling performance, the discharge coefficient, and aerodynamic loss should be considered to apply the film-cooling hole to the modern gas turbine blade's cooling design. The present study describes the discharge coefficients and aerodynamic loss characteristics for cylindrical and cratered holes with a numerical method. The shear stress transport turbulence model is firstly validated in comparison with the literature data. The discharge coefficients, total pressure coefficients, mixing pressure coefficients, and hole pressure coefficients are further determined under the coolant channel outlet's static pressure. The flow fields and velocity distributions of three coolant crossflow orientation configurations, including the co-flow orientation, the counter-flow orientation, and the perpendicular-flow orientation, are analyzed and compared. The numerical results show that the cratered hole always yields a higher discharge coefficient than the cylindrical hole, especially under the low-pressure ratio. The discharge coefficient is highly sensitive to the coolant crossflow orientation, mainly caused by the different separation flow at the hole entrance. The perpendicular-flow orientation configuration has the medium value of the discharge coefficient. For aerodynamic loss valuation, the cratered hole has a higher total pressure loss coefficient and pressure loss coefficient in the hole, but lower mixing pressure loss coefficient. The coolant flow orientation also influences these three pressure loss coefficients for the cylindrical hole and cratered hole, which can be explained by analyzing the flow field around the hole exit.