Boundary Layer and Loss Measurements on the Rotor of an Axial-Flow Turbine

The aerodynamic efficiency of an axial-flow turbine is significantly less than that predicted by measurements made on equivalent cascades which operate with steady inflow. This difference in efficiencies is strongly dependent upon the rotor-stator axial spacing. An experimental investigation of the rotor-stator interaction has therefore been conducted using a large-scale, low-speed turbine. The blade profile loss and surface shear stresses are presented for the midspan of the rotor and for a rectilinear cascade of identical geometry. Both wind tunnels were operated at a Reynolds number of 3.15 × 105. The turbine rotor midspan profile loss was approximately 50 percent higher than that of the rectilinear cascade. The shear stress measurements indicate that as a stator wake is connected through a rotor passage, the laminar boundary layers undergo transition in the vicinity of the wake. The 50 percent increase in loss is due to the time-dependent transitional nature of the boundary layers.