Experimental and numerical investigations on the influences of hole configuration and density ratio on endwall film cooling characteristics

Abstract

In present research, advanced cooling technologies combining upstream slot purge and discrete film cooling in the cascade passage were implemented. Experimental investigations employing pressure sensitive paint (PSP) techniques revealed distinct cooling performance correlated with flow characteristic. Under the conditions of different hole configurations (cylindrical holes and fan-shaped holes) and density ratios (DR = 1.0, 1.5 and 2.5), flow field and heat transfer coefficient were obtained by validated simulations to reveal the mechanism of vortices disturbance and heat transfer enhancement. Based on the data acquired by PSP, a modified film cooling superposition method was proposed to improve predicted accuracy for combined cooling effectiveness of slot purge and jets from discrete film holes. Results indicate that fan-shaped holes provide better film coverage thanks to suppress of coolant lift-off when DR = 1.0, with increase of DR, rapid reduction of momentum leads to sharp decline of film coverage area and cooling effectiveness. When DR = 2.5, coolant flowing out through cylindrical film holes performs higher ability to resist the influence of secondary flow because of higher momentum. As DR increases, the intensified disturbance from the passage vortex further disrupts the coolant, which significantly enhances heat transfer on the endwall, particularly around the third row of film holes, this localized heat transfer enhancement contributes to net heat flux ratio (NHFR) exceeding unity. The modified superposition method takes into account the influences of hole configurations and density ratios, which improves the accuracy of prediction for combined cooling effectiveness of slot and discrete film holes, and averaged relative error reduces from 0.2 to less than 0.1 when 0 < x/C_ax < 1.1 compared to Sellers’ superposition method.