FILM-COOLING WITH COMPOUND ANGLE HOLES - HEAT-TRANSFER

Heat transfer coefficients have been measured for film cooling injecti on from a single row of holes laterally directed with a compound angle of 60 deg. Two hole configurations were tested round holes and holes with a diffusing expansion at the exit. Streamwise-directed round hole s were also tested as a basis for comparison. All the holes were incli ned at 35 deg with respect to the surface. The density ratio was 1.0, momentum flux ratios ranged from I = 0.16 to 3.9, and mass flux ratios ranged from M = 0.4 to 2.0. Results are presented in terms of h(f)/h( 0), the ratio of film cooling heat transfer coefficient nt to the heat transfer coefficient for the undisturbed turbulent boundary layer at the same location. Results indicate that for the streamwise directed h oles, the heat transfer rates are close to the levels that exist witho ut injection. Similarly, at low momentum flux ratio, holes with a larg e compound angle had little effect on heat transfer rates However, at high momentum flux ratios, holes with a large compound angle had signi ficantly increased heat transfer levels. The results were combined wit h adiabatic effectiveness results to evaluate the overall performance of the three geometries. It is shown that for evaluation of film cooli ng performance with compound angle injection, especially at high momen tum flux ratios, it is critical to know the heat transfer coefficient, as the adiabatic effectiveness alone does not determine the performan ce. Compound angle injection at high momentum flux ratios gives higher effectiveness values than streamwise-directed holes, but the higher h eat transfer levels result in poorer overall performance.