Experimental study on film cooling performance of a turbine blade tip with a trapezoidal slot cooling scheme in transonic flow using PSP technique

A turbine blade tip with a trapezoidal slot cooling scheme is first proposed in the current paper. The film cooling characteristics of a turbine blade tip with a trapezoidal slot scheme are experimentally studied by the pressure sensitive paint (PSP) technique in transonic flow. Varieties of density ratio, tip clearance gap and position of the trapezoidal slot scheme are selected as investigation parameters. The mainstream Reynolds number is 370,000 based on the blade axial chord length. The cascade exit Mach numbers are is 1.05. The results indicate that increasing the density ratio has a positive effect on the film cooling effectiveness of the whole blade tip with a pressure side trapezoidal slot scheme at a small tip clearance gap, whereas it decreases the film cooling effectiveness upstream of the blade tip at the large tip clearance gap. For the blade tip with a pressure side trapezoidal slot scheme, the film cooling effectiveness of the tip clearance gap of 1.5% near the trailing edge is higher than that of the other tip clearance gaps at the same density ratio condition. Changing the trapezoidal slot position from the tip pressure side to the tip midline increases the film cooling effectiveness near the trailing edge.