Experimental Characterization of Unsteady Forces Triggered by Cavitation on a Centrifugal Pump

The present paper illustrates the results of recent experiments carried out under ESA funding in the Cavitating Pump Rotordynamic Test Facility (CPRTF) for the dynamic characterization of cavitation-induced flow instabilities as simultaneously observed in the stationary and rotating frames of a typical inducer for space propulsion applications. Specifically, the data refer to a three-bladed, tapered-hub, variable-pitch, "RAPDUD" inducer, designed by means of the reduced order model recently developed by the author and his collaborators for the geometric definition and performance prediction of this kind of hydraulic turbomachinery. Flow instabilities and their dynamic features have been detected, identified and monitored by means of the spectral analysis of the pressure measurements simultaneously generated in the absolute and relative frames by transducers respectively mounted a suitable locations on the casing and the hub of the test inducer. The comparison of the results obtained in the two reference frames over a wide range of flow coefficients and cavitation numbers contributed to better describe and understand the complex flow phenomena occurring in the blade channels of typical space inducers in the presence of cavitation-induced instabilities.