Inducer and Centrifugal Pump Contributions to the Rotordynamic Fluid Forces Acting on a Space Turbopump

The experimental characterization of the rotordynamic fluid forces acting on a whirling centrifugal impeller have been investigated at different flow rates and cavitating conditions. The recently developed method for continuously measuring the rotordynamic forces at variable whirl ratios has been readapted and successfully applied for measuring the same forces at constant whirl ratio but variable cavitation number. The flowrate has a major influence on the stability of the rotordynamic forces at positive whirl ratios where a threshold flowrate separates the stable zone from the unstable. At negative whirl ratios, the normal force is typically unstable independently on the flow rate. Cavitation has always a destabilizing effect at positive whirl ratio while it can stabilize the rotordynamic forces at negative whirl ratio.