Heat Transfer Performance of Fan-Shaped Film Cooling Holes: Part I—Experimental Analysis

Fan-shaped holes are widely used to provide better cooling performance than cylindrical holes over a large range of different operating conditions. Main advantages of such solution include a reduced amount of cooling air for the same performance, increased part lifetime, and fewer required holes. As the overall cooling performance of such holes is strictly related to the adiabatic effectiveness and heat transfer coefficient (HTC) increase due to the coolant injection, both issues should be investigated. In this paper detailed measurements of HTC and adiabatic effectiveness at different blowing ratios, between 0.50 and 2.50, for a single hole on a flat plate surface are presented. Results have been obtained for two laidback fan-shaped holes (called SAA and PAA) with different area ratio. In order to take into account the effects of pressure gradients caused by airfoil curvature, experiments are performed in two different mainstream flow conditions. The former without pressure gradient, the latter with a pressure gradient generated by an inclined opposite wall, with a positive acceleration parameter (K = 2.0·10⁻⁶). Both HTC and cooling effectiveness are measured using a steady state technique with wide band Thermo-chromic Liquid Crystals (TLC). A thin Inconel heating foil was used to generate a uniform surface heat flux for the HTC measurements. Results are presented in terms of detailed maps, centerline and spanwise averaged values.