An agitator rig is built to observe the unsteady characteristics of the large vortex produced by the rotor-stator interaction in impeller machinery. Using a PIV, a speeder and an encoder, the instantaneous velocity measurement is finished at a group of rotating speeds and phase angles, respectively. The ensemble averaged velocity, vortex streamline and turbulent intensity are obtained from PIV data. The results show that the distribution of the instantaneous parameters has no periodicity. The ensemble-averaged vortex is mainly located in the neighborhood of the static vanes, and the phase angle has little influence on it. The turbulent intensity has similar characters with the vortex.
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