Aerodynamics of a Low Pressure Turbine Airfoil at Low Reynolds Numbers—Part II: Blade Wake Interaction

Abstract

Part II of this twopart paper presents the aerodynamic behavior of a lowpressure highlift turbine airfoil, PakB, under the influence of incoming wakes. The periodic unsteady effects of wakes from a single upstream bladerow were measured in a lowspeed linear cascade facility at Reynolds numbers of 25,000, 50,000 and 100,000 and at two freestream turbulence intensity levels of 0.4% and 4%. In addition, eight reduced frequencies between 0.53 and 3.2, at three flow coefficients of 0.5, 0.7 and 1.0 were examined. The complex wakeinduced transition, flow separation and reattachment on the suction surface boundary layer were determined from an array of closelyspaced surface hotfilm sensors. The wakeinduced transition caused the separated boundary layer to reattach to the suction surface at all conditions examined. The timevarying profile losses, measured downstream of the cascade, increased with decreasing Reynolds number. The influence of increased freestream turbulence intensity was only evident in between wakepassing events at low reduced frequencies. At higher values of reduced frequency, the losses increased slightly and, for the cases examined here, losses were slightly larger at lower flow coefficients. An optimum wakepassing frequency was observed at which the profile losses were a minimum.