Validation of Transition Prediction of Baseline and High-Lift Airfoils in a Low Speed Cascade

Abstract

Abstract Due to the high cost of fuel, mitigation methods to reduce the engine weight while improving efficiency are necessary. One method for reducing engine weight includes a reduction in airfoil count. However, this approach can have the potential for added risk due to increased losses at off-design conditions. For the low-pressure turbine, the low Reynolds number off-design conditions become particularly of concern for increased loss generation. This current paper focuses on the validation of transition predictions for two low-pressure turbine airfoils using linear turbine cascade data. The baseline airfoil had a Zweifel loading coefficient of 1.1, and this airfoil was re-designed at a higher pitch spacing to increase the loading to 1.3. The experimental data includes pressure loadings at various Reynolds numbers ranging from 20K to 200K as well as loss measurements to quantify the Reynolds lapse rate at two levels of incoming turbulence. Additional tests for the high lift airfoil included simultaneously acquired suction surface hot film and midspan PIV data at two low Reynolds numbers and three different turbulence intensities. Comparisons between the Reynolds lapse rate of the baseline and increased lift airfoil show it is possible to increase the lift on the airfoil while only marginally increasing the loss for two turbulence conditions. Suction-side reattachment locations are indicated by three different methods: airfoil loading using Cp, suction surface hot film data, and midspan particle image velocimetry (PIV). These are in turn compared to results of flowfield simulations using a commercial solver where the Langtry-Menter Transition model was employed. Overall, the flowfield simulations for both airfoils compared favorably with experimental data for the Reynolds lapse rate as well as boundary layer separation and reattachment points on the suction surface at low Reynolds numbers.