Rocket turbopumps sometimes experience self-excited shaft vibration due to rotordynamic forces. To prevent this vibration, a key step is to establish a method to measure and evaluate the rotordynamic forces that act on turbopump components. In this study, we measured rotordynamic forces acting on a two-stage inducer using a rotordynamic test stand developed in 2012 at Kakuda Space Center. In noncavitating conditions, we did not observe strong nonlinearities in rotordynamic forces in the inducer at low flow rate conditions. The results of the pressure fluctuation on the inducer showed that rotordynamic forces were mainly excited in the second stage of the inducer. In cavitating conditions, we found that there is no strong nonlinearity between cavitating rotordynamic forces and the whirling frequency ratio in the inducer. These results show the robustness of the rotordynamic forces acting on the inducer against the flow rate and cavitation.

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