Time-Averaged Aerodynamics of a High-Speed Low-Pressure Turbine Cascade With Cavity Purge and Unsteady Wakes

Abstract

The time-averaged aerodynamics of a high-speed low-pressure turbine (LPT) cascade were investigated under the impact of unsteady wakes and purge flows. The tests were performed at an outlet Mach (M) and Reynolds numbers (Re) of 0.90 and 70 k, respectively. Unsteady wakes were simulated by means of a spoked-wheel type wake generator (WG), and a reduced frequency of 0.95 was achieved. The development of a purge flow system to operate at low-pressure levels is presented alongside guidelines for the operation of the circuit. The new purge system was commissioned in terms of its long-term stability and flow uniformity at the cascade inlet. The impact of varying purge flows from a cavity versus a flat endwall was assessed by means of static pressure measurements on the blade pressure side (PS) and suction side (SS) and traverses performed downstream with a miniaturized multi-hole probe. Differences in the secondary flow structures resultant from injecting purge flow into the flowfield are observed, namely, the intensification of the trailing shed vortex (TSV) and passage vortex (PV) that is also displaced away from the endwall. An increase of the endwall losses occurs as the flat endwall was replaced with a cavity geometry and the cavity purge flowrate increases.