Influence of Blade Loading Profile on Wake Dynamics in High-Pressure Turbine Cascades

Abstract

The influences of blade loading profile on wake convection and wake/wake interaction were studied in two different blade designs for high-pressure turbines (front-loaded and aft-loaded), installed in linear cascades. A high-speed moving bar apparatus replicated wake shedding, and a closed loop wind tunnel produced engine-relevant Mach numbers (Ma = 0.7) and Reynolds numbers (Re = 3 × 105). The front-loaded blades had approximately 10% greater total pressure loss when operated with unsteady wake passage. Phase conditioned PIV measurements were made in the aft portion of the blade channel and downstream of the blade trailing edge. The turbulence kinetic energy (TKE) in the wake was approximately 30% higher for the front-loaded blades when the wake entered the measurement field-of-view. The pressure field in the upstream region of the front-loaded blade design is believed to induce high magnitude strain rates — leading to increased TKE production — and more aggressively turn and dilate the unmixed wake — leading to increased mixing related losses. The higher TKE for the front-loaded blades largely dissipated by the time the wake reached the end of the blade passage. The interaction of the convected wake with the wake from the blade trailing edge caused periodic vortex shedding at the second harmonic of the convected wake frequency. This interaction also modulated the strength of the trailing edge wake. However, little difference was found in the modulation amplitudes between the different cases due to similar strengths of the convected wakes in this region. The higher wake TKE in the upstream portion of the blade channel for the front-loaded blades therefore is expected to be the cause of the increased total pressure loss.