Film Cooling for Slot Injection in Separated Flows

This experimental work is to investigate film cooling for slot injection in separated flows. The purpose of this research is to study the feasibility of a highly loaded very thin turbine blade which has been devised in order to reduce weight and to save the coolant amount by simplifying the complicated internal cooling passages. With such a thin airfoil, a considerable flow separation is expected to occur on the pressure-side and film cooling practice in that kind of flow field has not been well established. In order to clarify the film cooling mechanism in the separated flows, experiments with a simple back-facing step flow with a single slot injection simulating the separated pressure-side flows were carried out. Very high lip thickness to slot height ratio up to 8 was considered. Adiabatic effectiveness as well as velocity and turbulence profiles downstream of the step was measured in detail. The experimental results showed that there is a clear improvement in the film effectiveness with the largest lip thickness case for whole range of the tested blowing ratio. The flow field measurements suggested that a large recirculation zone acted as buffer or resistance for flow mixing, which contributed to the improvement in the film effectiveness.Copyright © 2005 by ASME