CFD Predictions of the Frequency Dependence 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 at high frequency such that F ≈ 1 and F > 1. 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. 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. High frequency pulsed jet cases are compared to low frequency pulsed jets as well as steady jets at matched averaged blowing ratios, M = 0.25 and 0.50. Simulations were performed at ReD = 60000. A simple technique is shown that can effectively predict pulsed film cooling performance at low frequency, but the fluid dynamics becomes more complex at higher frequencies yielding frequency dependent results at F > 3.