Studying the Film Effectiveness of Transpiration Cooled Walls Using Pressure Sensitive Paint

This paper presents the performance of pressure sensitive paint (PSP) for the direct investigation of a transpiration cooled surface. This technique allows the quantification of the pressure distribution on a porous surface with blowing. Additionally, it can be used to detect where the coolant is on the surface, thus measuring the transport of molecular oxygen to a transpiration cooled surface. For highly turbulent flows, it can also be used to evaluate the film effectiveness. A porous aluminium sample was anodised and dip coated in a PSP luminophore solution. It was fitted into a flat plate model and exposed to a Mach 5 cross-flow in the Oxford High Density Tunnel. Tests were conducted with no coolant injection, air injection and with nitrogen injection at increasing blowing ratios. The film effectiveness of the transpiration cooled surface was obtained for several conditions at Re = 15.5 - 31.5 10^6/m and F = 0.001 - 0.002. The film effectiveness increases as the Reynolds number decreases and the blowing ratio increases, which is in good qualitative agreement with the literature. Furthermore, it shows the same features as a velocity map of the outflow