Experimental investigation on the influence of inclination angle on the film cooling performance of diffuser shaped holes

Experimental investigation has been performed to investigate the influence of inclination angle on the film cooling performance of two typical diffuser shaped hole configurations, including laidback hole and laidback fanshape hole, using transient liquid crystal measurement technique. Under very small blowing ratio, increase of inclination angle has very small influence on the film cooling effectiveness of laidback fanshape hole configuration. With the increase of blowing ratio, large inclination angle notably reduces its film cooling effectiveness, especially in the upstream region. For film cooling of laidback hole configuration, the increase of inclination angle reduces the film cooling effectiveness under small blowing ratio due to the lift-off of film jets, while produces better film coverage and higher film cooling effectiveness under larger blowing ratios in the downstream region due to the reattachment of lift-off film jets. The increase of inclination angle reduces the heat transfer coefficient for film cooling of laidback fanshape hole configuration in the upstream region. For film cooling of laidback hole configuration, heat transfer coefficient is higher in the upstream region for large inclination angle case due to the enhancement effect of strong counter-rotating vortex pair, while laidback hole with small inclination angle has relatively higher heat transfer coefficient in the downstream region. Under very large blowing ratio, the counter-rotating vortex pair produce two intensely enhanced heat transfer region of spindle shape for film cooling of holes with large inclination angle. From the aspect of heat flux ratio, increase of inclination angle is beneficial to the thermal protection of laidback hole film cooling under large blowing ratio. For both diffuser shaped hole configurations, holes with large inclination angle have larger discharge coefficient due to smaller aerodynamic loss in the hole.