Effect of Flow Acceleration on Mainstream-to-Coolant Flow Interaction for Round and Shaped Film Cooling Holes
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Film cooling flow fields under a favorable, mainstream pressure gradient have been experimentally investigated at various blowing and density ratios. Three dimensional velocity and vorticity distributions have been obtained above a flat plate with cylindrical holes ( = 30) and laidback, fanshaped holes ( = 30, = = 10) using the stereoscopic particle image velocimetry (S-PIV) technique. In a low speed wind tunnel, accelerating flows were studied with density ratios of 1 and 3. The effect of blowing ratio was also studied by varying the ratio from 0.5 to 1.5. With a flow acceleration parameter comparable to previous investigations, the effect of flow acceleration on these film cooling flows is presented. The flow field measurements were performed at two planes near the film cooling holes (x/d = 0 and the downstream edge) for both the round and shaped holes. These flow field measurements provide a foundation for understanding the flow interactions that produce various film cooling effectiveness and heat transfer coefficient distributions on the surface of the airfoil. The S-PIV measurements show that a favorable pressure gradient reduces jet separation and increases the width of the jet and counter rotating vortex pair. The effects are caused by the thinning of the boundary layer that occurs in favorable pressure gradient flows.
