An experimental study of film cooling effectiveness by using PIV and PSP techniques

An experimental study was conducted to investigate the performance of film cooling injection from a row of circular holes spaced laterally across a flat plate. A highresolution PIV system was used to conduct flow field measurements to reveal the tendencies of the coolant stream to remain attached to the test plate or to separate from it, and a Pressure Sensitive Paint (PSP) technique was used to map the distribution of the corresponding adiabatic cooling effectiveness on the surface of the test plate based on a mass-flux analog to traditional thermal effectiveness measurements. The effects of the density ratio between the cooling jet stream and mainstream flows, P, are investigated by performing isothermal experiments at fixed mass-flux ratios but using coolant streams of N₂ (P=0.97), air (P=1.00), and CO₂ (P=1.53). An accompanying analysis of alternative parametric scaling quantities, such as the momentum flux ratio I and bulk coolant-to-mainstream velocity ratio V_r, is performed to illuminate the extent to which this flow scenario can be described using purely kinematic means. It was found that those quantities that give more weight to P (M and then I) have more success to collapse data from varying P flows for relatively low coolant flow rates, while the bulk velocity ratio V_r may be used with some success to scale the effectiveness from jets of higher bulk velocity ratio.