Investigation on the Influence of Various Mainstream Pressure Gradients on the Film Cooling Performances of Cylindrical Hole and Expansion Shaped Holes

In the present paper, experimental and numerical investigations have been carried out on the film cooling characteristics of cylindrical hole, laid-back fan shaped hole and double-fan shaped holes in the presence of various mainstream pressure gradients. Three momentum ratios: 1, 2 and 4, were measured. The pressure gradients, especially the adverse pressure gradient, improve the jet coverage and the jet lateral spread for cylindrical hole film cooling and 45 degrees inclined double-fan shaped hole film cooling, especially under large momentum ratios. However, the effect of pressure gradient on the film cooling effectiveness of 90 degrees inclined double-fan shaped hole is different from that of 45 degrees inclined double-fan shaped hole. The film cooling effectiveness under favorable pressure gradient is the highest for 90 degrees inclined hole. The effect of pressure gradients on the film cooling effectiveness of laid-back fan shaped hole and 20 degrees inclined double-fan shaped hole is weak because of the jets' good attachment on the wall. For all the holes, the normalized heat transfer coefficient h/h(0) under favorable mainstream pressure gradient is the highest under all the momentum ratios. Relative to the h/h(0) of zero pressure gradient, the h/h(0) of adverse pressure gradient is lower or close in the upstream region, but higher in the downstream region.