Study on Additive Effect of Film Cooling Effectiveness in Two Rows of Fan-Shaped Holes

Abstract The coolant jet interaction has a great influence on the superposition prediction of multirow film cooling. Although there have been many efforts to reveal the mechanics of additive effect in multirow film cooling, the available knowledge about developing the superposition method is still limited. The present work examines the film cooling effectiveness in two rows of fan-shaped holes by pressure sensitive paint technique, at the blowing ratios of 0.5 to 2.0 and the density ratio of 1.0. It is found that the impact of upstream flow on the downstream cooling film is reflected in the variation of turbulence intensity. The enhanced turbulence intensity is detrimental to the downstream film cooling effectiveness especially at the far away region. The mixing of upstream flow and coolant ejection starts at the leading edge of the hole exit. Thus, the streamwise width of the hole exit should be taken into consideration for better predicting the film cooling effectiveness around the holes. The cause of additive effect is that the coolant ejection at the second row affects the local mainstream entrainment. Then, a new correction factor, which characterizes the influence of coolant ejection on the mainstream entrainment of the upper row, is proposed for improving the classical Sellers method. The final result shows a good agreement with experimental data.