Optimized inlet geometry of a laidback fan-shaped film cooling hole - Experimental study of film cooling performance

The orientation of an internal coolant channel with respect to the external hot gas flow has a major impact on film cooling performance. Previous studies reported a considerable decrease of cooling performance with perpendicular coolant crossflow for a state-of-the-art laidback fan-shaped film cooling hole. The objective of this experimental study is to investigate the extent to which cooling performance in such a setup can be improved by using an optimized cooling hole inlet geometry. For this purpose, three geometries with different cooling hole inlets are investigated. Results are compared to a baseline geometry with a sharp-edged cylindrical inlet. A test rig is used which enables compliance with all relevant non-dimensional parameters. High-resolution infrared measurements are conducted and heat transfer as well as cooling effectiveness are evaluated for up to 50 cooling hole diameters downstream of the cooling hole exit. Results show that the cooling hole inlet geometry tremendously affects cooling performance. Diffuser aerodynamics are altered for all investigated geometries with a modified inlet. This leads to a more symmetrical pattern of the film cooling jet for two of the investigated geometries. As a consequence, film cooling effectiveness is increased compared to the baseline case. The disadvantages of a perpendicular coolant flow in terms of effectiveness are entirely eliminated. Additionally, heat transfer coefficients are lowered. An overall evaluation reveals that the heat flux into the wall is significantly reduced for the proposed optimized cooling hole geometries. (C) 2018 Elsevier Ltd. All rights reserved.