Experimental Study of Film Cooling With Favorable and Adverse Pressure Gradients

Film cooling experiments were conducted on a flat wall subject to favorable and adverse pressure gradients with a constant acceleration parameter, K. The test wall included a single row of five round holes in line with the flow direction and inclined at 35 deg to the surface. The hole spacing was 3 diameters. The wall opposite the test wall was moveable and was set to angles with respect to the test wall that produced K values of −0.5 × 10−6, 0, 1 × 10−6, 2 × 10−6, 2.5 × 10−6, and 3 × 10−6. Blowing ratios of 0, 0.5, 1, and 1.5 were tested at each acceleration. The test wall was equipped with constant flux surface heaters, and data were acquired for each flow condition with the wall both heated and unheated. An infrared camera was used to record wall temperature in a region spanning the three center holes and extending 20D downstream of the holes. From these measurements, local film cooling effectiveness and heat transfer coefficients were determined. In the flow, velocity and temperature profiles were acquired using hot-wire anemometry and a traversing thermocouple probe. Particle image velocimetry was used to acquire velocity fields in a plane perpendicular to the flow direction and 10D downstream of the holes. The pressure gradient had a noticeable effect on the flow, with the favorable pressure gradient reducing liftoff and moving the film cooling jets closer to the wall and reducing turbulence levels in the boundary layer. The adverse pressure gradient had the opposite effect. Near the wall, however, the effects of the pressure gradient on the film cooling effectiveness and heat transfer were more subtle.