Numerical investigation of pressure fluctuation in turbopump under off-design condition

High reliability of a turbopump should be guaranteed in wide speed range. However, abnormal vibration is occurred at 0.75 designed flow rate condition(Q_BEP). It is difficult to observe the flow field of this turbopump by experiment. To analyze the reason of the vibration, the steady and unsteady numerical simulation were conducted by using the SST model, and the cavitation was considered as well. The results show that 0.75Q_BEP is near the region of positive slope in the performance curve. Back flow and vortex were observed in the impeller passages. Cavitations are occurred at the inducer inlet and impeller inlet. Pressure fluctuations distributed continuously from 500~1440Hz are induced by impeller inlet cavitation, and the rotor-stator interaction accounts for pressure fluctuations of impeller rotational frequency, blade passing frequency and both their multiple frequency. Pressure fluctuations caused by impeller inlet cavitation are sensitive to the axial distance between inducer and impeller, and the fluctuation intensity reduces clearly when this distance is around 5mm.