Numerical and Experimental Investigation of the Film Cooling Effectiveness and Temperature Fields Behind a Novel Trench Configuration at High Blowing Ratio

Abstract

The present study is a numerical and an experimental investigation of film cooling from cylindrical holes embedded in a 0.75D deep transverse trench. Additionally, a new design with tetrahedral elements located upstream of the trench was examined. They interact with the approaching boundary layer and modify the flow field near the trench. Different heights of the tetrahedrons were considered. Results from all geometries were compared to those from a cylindrical hole. The experiments were performed in a heated closed loop wind tunnel with a coolant supply at cryogenic temperatures. The adiabatic film cooling effectiveness was obtained using infrared thermography. Temperatures within the flow field were measured using a cold-wire. The experiments were performed at four blowing ratios (1.0, 2.0, 3.0 and 4.0) and two density ratios (1.19 and 1.75). CFD simulations using FLUENT were carried out in order to investigate the developing flow field. The results show that the cooling effectiveness of the trench configuration increases with increasing blowing ratio. The coolant film remains attached to the surface even at the highest blowing ratio. In comparison to the original trench configuration the adiabatic effectiveness is enhanced by the tetrahedral elements due to reduced mixing of coolant and hot gas within the trench and improved lateral spreading of cooling air. The variation of the density ratio showed that the measurements can not be scaled with the blowing ratio alone without considering the density ratio.