Film Cooling Performance of Tripod Holes on the Endwall Upstream of a First Stage Nozzle Guide Vane

Abstract

In view of the growing energy demand, there is an increasing need to augment the thermal efficiency of gas turbine engines. The thermal efficiency and power output of gas turbine engines increase with increasing overall pressure ratio which in turn leads to an increase in turbine inlet temperature. The maximum permissible turbine inlet temperature is limited by the material strength of the components of the gas turbine engines. In this regard, it is important to ensure that the endwalls of the first stage nozzle guide vane, which is one of the critical regions, are adequately cooled. The cooling of the endwall is of particular interest because the leading edge region along the endwall of the stator vane experiences high heat transfer rates resulting from formation of horseshoe vortices. In this paper, the performance of upstream purge slot has been compared against discrete film cooling holes. Three different cooling configurations — slot, cylindrical holes and tripod holes have been investigated by comparing the adiabatic film cooling effectiveness. Furthermore, the effect of coolant to mainstream mass flow ratio on the effectiveness of the different cooling schemes has also been studied. The steady-state experiments were conducted in a low speed, linear cascade wind tunnel. Spatially resolved temperature data was captured using infrared thermography technique to compute adiabatic film cooling effectiveness. Amongst the configurations studied, slot ejection offered the best cooling performance at all mass flow ratios. The performance of tripod ejection was comparable to slot ejection at mass flow ratios between 0.5 and 1.5, with the difference in laterally averaged effectiveness being ∼5%. However, at the highest mass flow ratio (MFR=2.5), the difference increased to ∼20%. Low effectiveness values were observed downstream of cylindrical ejection which could be attributed to jet lift-off.