Abstract

Detailed pressure measurements were acquired at an axial chord Reynolds number of 20,000 with 3% inlet free stream turbulence intensity to study the effects of position and phase of vortex generator jets employed in an aft-loaded low-pressure turbine cascade in the presence of impinging wakes. Two-dimensional particle-image-velocimetry measurements were made at selected phases of the wake-passing period to investigate the temporal and spatial evolution of coherent spanwise structures and assess their roles in achieving optimal separation flow control. Impinging wakes thin the separation zone and delay separation by triggering transition in the separated shear layer. Though the frequencies differ by orders of magnitude, the vortex shedding from within the separation aligns with the wake forcing frequency. Effective separation control was achieved by pulsing a row of discrete vortex generator jets (VGJs) at a jet penetration threshold location buried within the uncontrolled separation. Synchronization with the periodic wake passing frequency was critical to produce the most effective separation control and recover the cascade’s high Reynolds number performance.

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