Film Cooling with Forward and Backward Injection for Cylindrical and Fan-shaped Holes Using PSP Measurement Technique

A systematic study was performed to investigate the combined effects of hole geometry, blowing ratio, density ratio and free-stream turbulence intensity on flat plate film cooling with forward and backward injection. Detailed film cooling effectiveness distributions were obtained using the steady state pressure sensitive paint (PSP) technique. Four common film-hole geometries with forward injection were used in this study: simple angled cylindrical holes and fan-shaped holes, and compound angled (? = 45?) cylindrical holes and fan-shaped holes. Additional four film-hole geometries with backward injection were tested by reversing the injection direction from forward to backward to the mainstream. There are seven holes in a row on each plate and each hole is 4 mm in diameter. The blowing ratio effect is studied at 10 different blowing ratios ranging from M = 0.3 to M = 2.0. The coolant to main stream density ratio (DR) effect is studied by using foreign gases with DR = 1 (N2), 1.5 (CO_2), and 2 (15% SF6 + 85% Ar). The free stream turbulence intensity effect is tested at 0.5% and 6%. The results of the parametric effects to the film cooling effectiveness with forward injection agreed with open literatures. In general, the results show the film cooling effectiveness with backward injection is greatly reduced for shaped holes as compared with the forward injection. However, significant improvements can be seen in simple angled cylindrical hole at higher blowing ratios. Backward injection also shows improvements at near film-hole regions for compound angled cylindrical holes at higher blowing ratios. Comparison was made between the experimental data and empirical correlation for simple angled fan-shaped holes.