Effect of film hole location on heat transfer coefficient and film effectiveness of a gas turbine blade

Abstract

Experiments were performed to study the effect of film hole location on local heat transfer coefficient and film effectiveness distributions of a turbine blade model with air (D.R. = 1.0) and C02 (D.R. = 1.52) film injection. Tests were performed on a five blade linear cascade at the chord Reynolds number of 3x 105 at the cascade inlet. The test blade had three rows of film holes in the leading edge region and two rows each on the pressure and suction surfaces. Film hole locations were varied by leaving the desired holes open and plugging the others. A combination of turbulence grid and unsteady wake was used to generate unsteady high turbulence upstream conditions. The results show that film injection by itself causes a substantial increase in Nusselt numbers over a blade model without film holes. An increase in mainstream turbulence intensity causes an increase in Nusselt number and a decrease in film effectiveness, for both density injectants, and at all studied blowing ratios. Film injection promotes an earlier transition and the onset of transition depends on the film injection location; but at high turbulence levels, transition location is nearly independent of film injection location. The results also indicate injection at different locations provides different film effectiveness, depending on the local mainstream velocity and blade curvature. In addition, the superposition model of film effectiveness has been examined by comparing the measured film effectiveness with predictions using this model. For most cases, the superposition principle accurately predicts the film effectiveness downstream of the injection region.