Net Heat Flux Reduction for Pulsed Film Cooling on a Turbine Blade Leading Edge

Abstract

Film cooling is used to protect components in the hot gas path of a gas turbine engine from the high temperature main flow. In addition to reducing the adiabatic wall temperature, film cooling generally increases the heat transfer coefficient, thereby partially offsetting the benefits in reduced adiabatic wall temperature. Adiabatic effectiveness and heat transfer coefficient are often combined to predict the net heat flux reduction due to film cooling in a steady film flow. Unsteadiness in film flow, however, may arise due to inherent unsteadiness in the external flow or may be intentionally induced as a means of flow control. In the present study, we make use of a new experimental technique to analyze the performance of unsteady film cooling on the leading edge of a turbine blade. The net heat flux reduction with pulsed film cooling is measured and 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. For a single coolant hole located 21.5° from the leading edge, angled 20° to the surface and 90° to the streamwise direction, measurements indicate that steady film flow is generally desirable relative to pulsed film cooling. However, at high average coolant flow rates beyond the optimum blowing ratio, pulsing the film cooling jet can be advantageous. Measurements were made at freestream Reynolds numbers of ReD = 60k and 30k, each with two different turbulence intensities.