CFD Predictions of Pulsed Film Cooling Heat Flux on a Turbine Blade Leading Edge

Abstract

Unsteadiness in film cooling jets may arise due to inherent unsteadiness of the blade-vane interaction or may be induced as a means of flow control. A computational study was conducted to determine how leading edge film cooling performance is affected by pulsing the coolant flow. A cylindrical leading edge with a flat afterbody is used to simulate the turbine blade leading edge region. A single coolant hole was located 21.5° from the leading edge, angled 20° to the surface and 90° from the streamwise direction. The leading edge diameter to hole diameter ratio is D/d = 18.7. Time resolved adiabatic effectiveness and heat transfer coefficient are used to calculate the temporally averaged, spatially resolved net heat flux reduction for several pulsing scenarios. The net heat flux reduction with pulsed film cooling is compared to the steady jet with matched average mass flow rate. Steady blowing ratios of M = 0.25 and 0.50 are each compared with two pulsed jet cases with matching averaging blowing ratio, M, at a nondimensional frequency, F = 0.151 and duty cycle, DC = 50%. Simulations were performed at ReD = 60000. Net heat flux is generally increased by pulsing the film coolant, with greater degradation for higher pulsation amplitudes relative to the average blowing ratio.