Particle Image Velocimetry Characterization of High-Speed Centrifugal Compressor Impeller-Diffuser Interaction

Abstract

High-density instantaneous and rotor phase-locked velocity field measurements are made in the centrifugal compressor diffuser vaneless space by means of the particle image velocimetry technique. The technique is challenged in this application by a small length scale and large velocities yielding very small flow time scales and demanding the use of extremely small flow tracking particles. The experiments reveal a detailed picture of the rotor phase-lockedaverageimpellerexitanddiffuserinlet flowfieldasisusefulforunsteady flowmodeling.Strongpassage velocity gradients exist across the vaneless space up to the diffuser vanes, showing that the phase-locked averaged impeller exit flow presents a highly unsteady non-mixed-out velocity field for the downstream vane row. This unsteady vane intake is thus characterized by a strong fluctuation in incidence angle with the passing blade event. Measured time variation in the velocity field indicates a significant time-varying potential field due to incidence fluctuations. Nomenclature Rduct = inlet duct radius r = radius � = radius ratio (diffuser leading-edge radius/impeller tip radius) � = 1 standard deviation