Net Heat Flux Reduction and Overall Effectiveness for a Turbine Blade Leading Edge

Abstract

The external cooling performance of a film cooled turbine airfoil can be quantified as a net reduction in heat transfer relative to the turbine airfoil without film cooling. This quantification is generally accomplished by using measurements of the adiabatic effectiveness and the change in heat transfer coefficients (hf/h0) for the film cooled surface to determine the net heat flux reduction (Δqr). Although measurement of Δqr for laboratory models give an indication of the ultimate film cooling performance, this does not show how much the surface temperature of the airfoil is reduced by film cooling. Measurement of scaled surface temperatures can be accomplished by using laboratory models constructed so that the Biot number is matched with that of the actual airfoil. These measurements provide a scaled temperature distribution on the airfoil that is referred to as the overall effectiveness, φ. For the current study, measurements of Δqr and φ have been made for a simulated turbine blade leading edge. The simulated leading edge incorporated shaped coolant holes, and had three rows of coolant holes. Improvements due to the shaped holes were determined by comparisons with previously measured round hole configurations. Spatially distributed hf/h0 show increases of 5% to 15% for M = 1.0 and 10% to 30% for M = 2.0. Results show that local variation in Δqr much greater than variation in φ, but laterally averaged Δqr distributions are reasonable predictors of the laterally averaged φ distributions.