Film Cooling in the Presence of Mainstream Pressure Gradients

Film cooling in the presence of mainstream pressure gradients typical of gas turbines has been studied experimentally on a flat plate. This paper describes measurements of the spanwise-averaged effectiveness and heat transfer coefficient for an inclined slot and a single row of holes in the presence of favorable, zero, and adverse pressure gradients. Acceleration parameters of K = 2.62 × 10⁻⁶ and −0.22 × 10⁻⁶ were achieved at the point of injection where the free-stream unit Reynolds number was held constant at Re/m = 2.7 × 10⁷. The flow was accelerated to high Mach number and results are analyzed using a superposition model of film cooling, which included the effects of viscous energy dissipation. The experimental results show that the effects of pressure gradient differ between the geometries and a discussion of these results is included. The unblown turbulent boundary layers with pressure gradient were also studied. Experiments were performed using the Isentropic Light Piston Tunnel, a transient facility that enables conditions representative of those in the engine to be attained.