Analysis of Flow Instabilities on a Three-Bladed Axial Inducer in Fixed and Rotating Frames

The paper describes the results of recent experiments carried out in the Cavitating Pump Rotordynamic Test Facility for the dynamic characterization of cavitation-induced flow instabilities as simultaneously observed in the stationary and rotating frames of a high-head, three-bladed axial inducer with tapered hub and variable pitch. The flow instabilities occurring in the eye and inside the blading of the inducer have been detected, identified, and monitored by means of the spectral analysis of the pressure measurements simultaneously performed in the stationary and rotating frames by multiple transducers mounted on the casing near the inducer eye and on the inducer hub along the blade channels. An interaction between the unstable flows in the pump inlet and in the blade channels during cavitating regime has been detected. The interaction is between a low frequency axial phenomenon, which cyclically fills and empties each blade channel with cavitation, and a rotating phenomenon detected in the inducer eye.