Effects of Periodic Unsteadiness on Secondary Flows in High Pressure Turbine Passages

Abstract

Secondary flow losses were investigated experimentally in a linear cascade of high pressure turbine blades in a low speed wind tunnel. Periodic wakes were generated with moving rods upstream of the cascade to simulate the effect of wakes from upstream vanes in an engine. Velocities, turbulence levels and turbulence spectra were documented downstream of the wakes generated by the upstream rods and downstream of the cascade airfoils. Pressure distributions were documented on the airfoils at the midspan and near the tip. Total pressure loss through the passage was measured at the midspan and in the endwall boundary layer. Cases were documented with and without upstream wakes at a Reynolds number of 30,000 based on inlet velocity and axial chord. An additional case was acquired at Re = 60,000 without wakes. The effects of wakes and Reynolds number on the pressure distribution on the airfoils were small. In the cases without wakes, total pressure losses were 27% higher at the lower Reynolds number due to thicker boundary layers. Upstream wakes cause an increase of about 80% in total pressure losses at the midspan and a 36% increase near the endwall. Much of this is due to the loss associated with the upstream wakes themselves, but with this direct effect subtracted the losses are still 20% higher in the case with wakes at the midspan with local increases comparable near the endwall.