Transient Liquid Crystal Measurement of Leading Edge Film Cooling Effectiveness and Heat Transfer With High Free Stream Turbulence

Abstract

This paper studies the film effectiveness and heat transfer coefficients on a large scale symmetric circular leading edge with three rows of film holes. The film hole configuration focuses on a smaller injection angle of 20° and a larger hole pitch with respect to the hole diameter (P/d = 7.86). The study includes four blowing ratios (M = 1.0, 1.5, 2.0 and 2.5), two Reynolds numbers (Re = 30,000 and 60,000), and two free stream turbulence levels (approximately Tu = 1% and 20% depending on the Reynolds number). The method used to obtain the film cooling effectiveness and the heat transfer coefficient in the experiment is a transient liquid crystal technique. The distributions of film effectiveness and heat transfer coefficient are obtained with spatial resolutions of about 0.6 mm or 13% of the film cooling hole diameter. Results are presented for detailed and spanwise averaged values of film effectiveness and Frössling number. Blowing ratios investigated result in up to 2.8 times the lowest blowing ratio’s film effectiveness. Increasing the Reynolds number from 30,000 to 60,000 results in increasing the effectiveness by up to 55% at high turbulence. Turbulence intensity has up to a 60% attenuation on effectiveness between rows at Re = 30,000. The turbulence intensity has the same order of magnitude but opposite effect as Reynolds number, which also has the same order of magnitude effect as blowing ratio on the film effectiveness. A crossover from attenuation to improved film effectiveness after the second row of film holes is found for the high turbulence case as blowing ratio increases. The blowing ratio of two shows a spatial coupling of the stagnation row of film holes with the second row (21.5°) of film holes which results in the highest film effectiveness and also the highest Frössling numbers.