PIV study of wake-rotor interactions in a transonic compressor at various operating conditions

Details of the unsteady flowfield between an upstream wake generator and a downstream rotor that are closely spaced in a transonic compressor are studied at various operating conditions using particle-image velocimetry. Flow-visualization images and particle-image velocimetry data facilitate analysis of the details of shed vortices, wake motion, and wake-shock interaction phenomena. Such analysis not only aids the understanding of the effect of blade-row interactions on compressor performance but also allows verification of time-accurate CFD codes that are used to characterize transonic compressors. As the operating point changes from choke to stall and the rotor-bow shock moves upstream, distinct vortex-shedding patterns are observed that affect the wake deviation and rotor incidence. With close spacing between the wake generator and the rotor, vortex shedding from the wake generator and the passage of the rotor-bow shock are strongly synchronized and blade-passage phase-locked measurements are possible. The resulting multiple images of the How corresponding to any blade position are averaged to yield vortex and rotor-bow-shock locations at various back pressures. Using various postprocessing methods, specific shed vortices and wake topological features are isolated and details of the wake-shock interaction are captured.