Experimental Characterization of the Rotordynamic Forces on Space Rocket Axial Inducers

The present paper illustrates the results of an experimental campaign conducted in the Cavitating Pump Rotordynamic Test Facility (CPRTF) at ALTA S.p.A. aimed at characterizing the rotordynamic forces acting on two different whirling tapered-hub, variable-pitch axial inducers. The forces acting on the impeller have been measured by means of a rotating dynamometer mounted just behind the inducer. The roles of the imposed whirl motion of the rotor, flow coefficient, cavitation number, and liquid temperature have been investigated. The destabilizing role of cavitation has been confirmed. The experimental results are consistent with previous experimental campaigns documented by the open literature, including the former data published by Caltech researchers. The observed dependence of the tangential and normal components of the rotordynamic force on the whirl-to-rotational speed ratio does not follow the quadratic functional behavior often assumed in the open literature. Rotordynamic forces of large amplitude and destabilizing nature especially occur in the presence of cavitation, potentially compromising the stability of the pump operation.