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In general, pressure sensitive paint (PSP) and thermochromic liquid crystal (TLC) are used to indicate film cooling efficiency. However, due to the mechanisms of PSP and TLC being different, their results are not consistent in some cases. Thus, analyzing the divergence between these two measurement methods is essential. In this paper, a comparison of measured film cooling efficiency distribution between PSP and TLC has been made on the same wind tunnel; the effect of heat conduction on film cooling was analyzed qualitatively and quantitatively. Sixteen cases were analyzed in which the mainstream Reynolds number was 35 000, 45 000, and 57 000; the blowing ratio was 0.5, 1.0, 1.5, and 2.0; and the density ratio was 0.91 and 1.44. We found that both PSP and TLC results exihibit an optimum blowing ratio under the condition of small and medium mainstream Reynolds numbers, but the measured film cooling efficiency is slightly different. Differences between PSP and TLC results were caused by the heat conduction of the substantial region. At the same time, a high mainstream Reynolds number and a high blowing ratio would boost heat conduction. Furthermore, in cases of high mainstream Reynolds number and low blowing ratio, the effect of heat conduction decreased obviously. When the blowing ratio is small as 0.5 and N2 acts as a coolant, PSP and TLC results match well, showing that in cases of low blowing ratio and low density ratio, the effect of heat conduction can be ignored.

This paper reports the experimental and numerical studies on the effects of rotating speed and blowing ratio on the film cooling performance of the hole near the leading edge on the suction side of the turbine blade. The chord and height of the blade are 60mm and 80mm respectively. The film hole with diameter of 0.8mm is located in the mid span on the suction side at axial location of 8%. The injection angle of the hole is 45° to the suction surface of the blade and is nearly perpendicular to the axial direction. Both experimental and numerical studies were carried out with rotating speeds of 300rpm, 450rpm and 600rpm, and with blowing ratios of 0.5, 1.0, 1.5 and 2.0. CO2 was used as the coolant. Experimental data was measured by applying the Thermochromic Liquid Crystal (TLC) technique and the Stroboscopic Imaging Technique. Mainstream and coolant were heated to 308K and 318K respectively. Numerical studies were performed to assist the analysis of the experimental results. The SST turbulence model was applied in the simulations. Results show that the film cooling performance of the hole near the leading edge is different from that of the hole further downstream on the suction side. This is because the direction of the jet is nearly perpendicular to the axial direction, which increases the effect of the Coriolis force. Besides, the mainstream from leading edge also has effects on film cooling performance. With the increase of the blowing ratio, the film coverage area and spatially averaged film cooling effectiveness increase first and then decrease. The maximum film coverage and averaged film cooling effectiveness appear at blowing ratio of 1.0 and rotating speed of 300rpm. Moreover, the upward deflection angle of the film trajectory increases slightly with the increase of the blowing ratio. Higher rotating speed intensifies the deflection of the film trajectory. Therefore, the film coverage and the averaged film cooling effectiveness decrease rapidly.