PIV Study of Blade-Row Interactions in a Transonic Compressor

Abstract

Details of the unsteady flow field between an upstream stator and a downstream rotor in a transonic compressor are obtained using Particle Image Velocimetry (PIV). Flowvisualization images and PIV data that facilitate analysis of vortex shedding, wake motion, wake deviation, rotor incidence, and wake-shock-interaction phenomena are presented. 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. The present investigation introduces new methods for PIV implementation in complex turbomachinery environments. The PIV measurements are synchronized with various rotor-blade locations, and the instantaneous and averaged velocity fields of the flow are calculated. Stator wake and rotor-bow-shock flow interactions in the blade row are identified for various stator/rotor axial spacings and operating conditions. Using various post-processing methods, specific shed vortices and wake topological features are isolated and details of the shock-wake interaction captured. At far spacing, the vortices shed from the stator are phase-locked and shed as counterrotating pairs in the wake. Rotor-bow-shock strength varied, depending on the axial gap between the stator and rotor and the operating condition. Results show that as the rotorbow-shock is chopped by the stator TE, it turns more normal to the stator pressure surface and propagates upstream, validating a prior significant observation made with timeaccurate CFD.