Inducer and centrifugal pump contributions to the rotordynamic fluid forces acting on a space turbopump

The fluid-induced rotordynamic forces acting on a whirling space turbopump composed by an inducer and a radial impeller have been compared to the same forces measured on each single component of the turbomachine (i.e., on the inducer and on the radial impeller). The experimental campaign has been carried out in cold water at design and offdesign conditions (80%, 100%, and 120% of the design flow rate) both in noncavitating (NC) and cavitating regimes. The paper illustrates the different trends of the rotordynamic forces on the axial and radial pumps and highlights their contributions on the overall turbomachine. At positive whirl ratios, the behavior of the inducer is dominant while, at negative ones, both the pumps show the same trends in such a way that the overall behavior is roughly the sum of each single component.