Measured overall effusion cooling effectiveness over a wide blowing ratio range using infrared imaging

Experimental investigations were performed on the overall cooling effectiveness η of a flat effusion wall over a wide range of blowing ratio (M=0.47~5.27). The effusion wall had a staggered multi-hole pattern typical of gas turbine combustor application, with a ratio of hole pitch to row spacing P/S=1:2, a porosity PS/d²=72, and an inclination angle α=30°. The current paper documented distribution of the overall cooling effectiveness on the wall surface, based on infrared imaging of the 2-D surface temperature field. Experimental results indicate: (1) The overall η increases along with the streamwise distance for the wide range of M due to the superposition effect of the multi-row film cooling. (2) The overall η substantially benefits from the multi-hole inside convective cooling. The hole convective cooling not only complements the weakest film protection at initial rows but also helps mitigate the temperature gradient. (3) The overall η increases asymptotically with increasing M, unlike adiabatic η mostly published in the past, which decreased after M reached a specific level. The current work showcased the end cooling outcome jointly driven by the filming cooling mechanism and the hole inside convective cooling mechanism.