Effect of Density Ratio on Flat Plate Film Cooling With Shaped Holes Using PSP

Detailed film-cooling effectiveness distributions are obtained on a flat plate using the pressure sensitive paint (PSP) technique. The applicability of the PSP technique is expanded to include a coolant-to-mainstream density ratio of 1.4. The effect of density ratio on the film-cooling effectiveness is coupled with varying blowing ratio $(M=0.25–2.0)$⁠, freestream turbulence intensity $(Tu=1–12.5%)$⁠, and film hole geometry. The effectiveness distributions are obtained on three separate flat plates containing either simple angle, cylindrical holes, simple angle, fanshaped holes $(α=10deg)$⁠, or simple angle, laidback, fanshaped holes (⁠$α=10deg$ and $γ=10deg$⁠). In all three cases, the film-cooling holes are angled at $θ=35deg$ from the mainstream flow. Using the PSP technique, the combined effects of blowing ratio, turbulence intensity, and density ratio are captured for each film-cooling geometry. The detailed film-cooling effectiveness distributions, for cylindrical holes, clearly show that the effectiveness at the lowest blowing ratio is enhanced at the lower density ratio $(DR=1)$⁠. However, as the blowing ratio increases, a transition occurs, leading to increased effectiveness with the elevated density ratio $(DR=1.4)$⁠. In addition, the PSP technique captures an upstream shift of the coolant jet reattachment point as the density ratio increases or the turbulence intensity increases (at moderate blowing ratios for cylindrical holes). With the decreased momentum of the shaped film-cooling holes, the greatest film-cooling effectiveness is obtained at the lower density ratio $(DR=1.0)$ over the entire range of blowing ratios considered. In all cases, as the freestream turbulence intensity increases, the film effectiveness decreases; this effect is reduced as the blowing ratio increases for all three film hole configurations.