Leading edge film cooling heat transfer with high free stream turbulence using a transient liquid crystal image method

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This paper studies 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 (nominally Tu=1% and 20% depending on the Reynolds number). A transient liquid crystal (LC) image technique is employed to obtain the film effectiveness and heat transfer coefficient distributions with high spatial resolutions of 0.6 mm in both streamwise and spanwise directions. Results are presented for detailed and spanwise averaged values of film effectiveness and Frössling number. Turbulence intensity has an attenuation on film effectiveness as well as on Frössling number for all blowing ratios at Re=30,000. Under high turbulence conditions the film effectiveness and Frössling number increase as blowing ratio increases from 1.0 to 2.0 for both Reynolds numbers. Further increasing the blowing ratio results in reverse effect. Increasing the Reynolds number from 30,000 to 60,000 results in increases in both the film effectiveness and Frössling number at high turbulence except for M=2.5. 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.