斜流式泵喷水推进器内部流动不稳定性分析

为了揭示斜流式泵喷水推进器的内部流动规律,利用多重参考系法,选用标准k-ε湍流模型和SIM-PLE算法,对不同工况下斜流式泵喷水推进器进行了数值模拟,分析了泵内部流动与其不稳定性之间的关系及叶轮叶片表面的压力分布规律.结果表明：扬程系数ψ与Q/Qbep曲线在流量为0.65Qbep～0.67Qbep工况下出现了正斜率（Q为工况点流量,Qbep为最佳设计工况点流量）,主要原因是导叶进口轮毂处的回流撞击叶轮出口流动,使其产生流动分离,最终形成旋涡,导致内部流动不稳定,从而使压力上升;在流量为0.65Qbep和0.85Qbep工况下,导叶内均出现回流,回流区域及回流速度随流量减小而增大.模拟分析说明斜流式泵喷水推进器在小流量工况下运行具有不稳定性.

Instability analysis of internal flow in mixed-flow pump waterjet propulsion

In order to reveal the internal flow characteristic of a mixed-flow waterjet propulsion,a mixed-flow waterjet propulsion under different conditions was simulated based on multi-reference frame(MRF),the standard k-ε turbulent model and SIMPLEC algorithm.The relationship between pump instability and internal flow and the pressure distribution on the surface of the impeller blade were obtained.The numerical results show that characteristic instability occurrs at 0.65Qbep～0.67Qbep(Q is the flowrate;Qbep is the flowrate at best efficiency point),the reason is that the backflow on the vaned diffuser hub-side blocks the downstream flow from the impeller.Therefore,the flow separates on the pressure surface of the impeller outlet and a strong vortex is generated,and then the pressure-rise appears due to the instability of internal flow.Backflow is found in diffuser passage at 0.65Qbep and 0.85Qbep,as flow rate decreases,the backflow region and velocity increases.According to the numerical simulation,the mixed-flow waterjet propulsion has a characteristic of instability at partial flow rate condition.