Film Effectiveness Downstream of a Row of Compound Angle Film Holes

Effects that two different compound-angle film-hole configurations have on film cooling effectiveness are investigated. Effectiveness measurements have been made downstream of a single row of compound-angle cylindrical holes with a diameter of 7.5 mm, and a single row of compound-angle, diffuser-shaped holes with an inlet diameter of 7.5 mm. Both geometries were inclined with respect to the coverage surface at an angle α of 25 deg. The cylindrical holes, however, were oriented perpendicular to the high-temperature airflow direction while the diffuser-shaped holes had a compound angle of 45 deg with respect to the high temperature air flow direction. Both geometries were tested over a blowing ratio range of 0.7 to 4.0 Surface temperatures were measured along four longitudinal rows of thermocouples covering the downstream area between two adjacent holes. The results showed that the best overall protection over the widest range of blowing ratios was provided by the diffuser-shaped film cooling holes, particularly at high blowing ratios. The increased cross-sectional area at the shaped hole exit lead to a reduction of the momentum flux of the jet exiting the hole. Therefore, the penetration of the jet into the main flow was reduced, resulting in an increased cooling effectiveness. CFD analyses were also performed to study the film cooling effectiveness downstream of the row of holes. Comparisons between the test and numerical results showed a reasonable agreement between the two, thus CFD can be considered a viable tool to predict the cooling performance of different film cooling configurations in a parametric study.