Comparison of Rotordynamic Fluid Forces Between Closed Impeller and Open Impeller

In the design of rocket turbopump with high energy density, rotordynamics considerations are very important to stabilize the motion of the shaft. Rotordynamic instabilities generated by rotordynamic fluid forces are often reported. It is recognized that the forces affect the whirling motion of the rotor, and induce the self-excited vibration. To understand the effect of the rotordynamic fluid forces of the impellers on rotor vibration, a tangential fluid force in a forward whirling direction and a normal fluid force in a radial direction were measured by using the experimental apparatus with an active magnetic bearing. As the experimental result for a closed impeller and an open impeller, it was clarified their fluid forces are quite different in the characteristics of destabilizing/damping effects and restoring/inertia effects.