Experimental Evaluation of High Lift, High Work LPT Blades in a Transonic Cascade

Abstract A family of low-pressure turbine stages was recently developed to investigate the limits of achievable work and lift for future engines applicable to unmanned air systems. Subsequently, mid-span sections of a pair of turbine blades from those stages were manufactured for testing in a transonic cascade facility to verify predicted performance at both on- and off-design conditions. Both turbine blades were designed at the meanline level to a work coefficient of 2.80, and the velocity triangles and pitch-to-chord ratios were consistent with incompressible Zweifel coefficients of 1.60 and 1.78. At design conditions, the airfoils provided 123° of flow turning at an exit isentropic Mach number of 0.78. Both inlet- and exit-total pressure traverses were conducted, and the inlet turbulence intensity and length scale were measured at a pair of locations upstream of the instrumented airfoils in the mid-passage. The experimental datasets presented herein include loading variations as well as loss variations versus Reynolds number. It was found that neither airfoil experienced separation at the lowest Reynolds number achievable at design exit Mach number. Accordingly, it was necessary to operate the cascade at reduced total-to-static pressure ratios to observe significant effects of separation on the loading and loss results. The experimental results presented here are compared against design-level predictions using Reynolds Averaged Navier-Stokes (RANS) codes with transition modeling as well as Large Eddy Simulation (LES). The results are encouraging and bode well for the development of future engines that have reduced part-count, weight, and cost while providing acceptable performance lapse at altitude.