涡轮泵非设计工况压力脉动数值研究

Numerical Investigation of Pressure Fluctuation in Turbopump Under Off-Design Condition

涡轮泵工作时要求在较宽转速范围内运行稳定,但实验中涡轮泵的泵部件在0.75QBEP工况下出现异常振动,由于结构限制,直接通过实验检测内部流动特性较困难.为探究其振动原因,采用SST湍流模型并考虑空化对该泵进行定常和非定常模拟,分析其内部流场和压力脉动特性.研究发现0.75QBEP工况靠近正斜率不稳定区,离心轮流道内存在回流、漩涡等不良流态;诱导轮和离心轮进口有空化现象发生.离心轮进口处空化引发的压力脉动在500 ～1440Hz范围内连续分布,动静干涉引发的压力脉动以转频、叶频及两者的倍频为主.改变诱导轮与离心轮轴向间隙对诱导轮与离心轮之间的压力脉动影响较为明显,对其他位置压力脉动影响较小,当间隙扩大到5mm左右时能在一定程度上改善0.75QBEP工况的异常振动.

High reliability of a turbopump should be guaranteed in wide speed range.However,abnormal vibration is occurred at O.75 designed flow rate condition(QBEP).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 0.75QBEp 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.