Film cooling performance on curved walls with compound angle hole configuration

In order to explore the effect of compound angle holes on film cooling over a convex wall and a concave wall, the present study adopts the transient liquid crystal thermography for conducting the film cooling measurement on simple hole and expanded-hole configurations. Two compound angles of 0 and 45 deg are tested at an elevated mainstream turbulence condition (Tu) of 3.8%. The test pieces have the different radius of curvature (2r/D) of 92.5 on convex and 86.5 on concave, and the same pitch to diameter ratio (P/D) of 3 on both convex and concave walls. All measurements were conducted under the mainstream Reynolds number (Re(d)) of 1700 on convex and 2300 on concave with the density ratio between coolant and mainstream (rho c/rho m) of 0.98. In current study, the effect of blowing ratio (M) on film cooling performance is investigated by varying the range of blowing ratio from 0.5 and 2.0. The present measured results show that the forward-expanded hole injection provides better surface protection than the simple hole injection. As far as the injection angle is concerned, compound angle injection provides higher film effectiveness than simple angle injection. However, the forward-expanded hole in injection (beta = 0 degree) has the best performance on both convex and concave surfaces.