导叶式混流泵多工况内部流场的PIV测量

为研究不同流量工况下混流泵内部流动特性,该文基于粒子图像测速技术(particle image velocimetry)对0.8、1.0、1.2倍流量工况下混流泵的内部流场进行试验研究,测量获得了混流泵叶轮进口轴截面、叶轮与导叶间隙和导叶内部流场的速度场分布,分析了流量变化对混流泵内部流动的影响。研究结果表明,外特性试验重复性较好,试验结果较为可靠。3个工况下混流泵叶轮进口流场的速度分布趋势基本一致,进口的来流基本沿着轴线方向;随着流量增加,叶轮进口速度不断增大,最大速度达到7.49 m/s,从轮毂到轮缘高速区域速度梯度更为明显,速度等值线分布逐渐形成以左上角为圆心,不断向周围递减的趋势。受动静干涉作用影响,叶轮与导叶间隙流场速度分布较为紊乱,在导叶进口边轮毂附近形成逆时针方向旋涡,诱使叶轮出口流体向外缘侧偏转;随着流量增加,逆向旋涡明显减小,内部流动更趋于平稳。动静干涉效应进一步影响导叶进口流场并形成明显的旋涡结构,造成流道堵塞;在导叶出口由于环形蜗室的影响形成大尺度旋涡结构;随着流量增大,导叶外缘高速区向下游移动,导叶进出口的旋涡结构逐渐消失,流动损失减小。研究成果为揭示混流泵内部流动特性和优化混流泵设计提供参考。

PIV measurement of internal flow in mixed-flow pump under different flow rate conditions

Abstract: In this study, a low specific speed mixed-flow pump with guide vanes was investigated experimentally. In order to study the internal flow characteristics in this mixed flow pump under different flow conditions, the internal flow of mixed flow pump under 0.8, 1.0, 1.2 times of the designed flow conditions were studied in this paper based on the particle image velocimetry (PIV) technology. Firstly, the external characteristics of mixed flow pump were acquired after conducting the repeated experiment. Then, the velocity distribution of internal flow field in mixed flow pump at inlet axial cross section of impeller, section clearance between impeller and guide vane and section in guide vane were measured. Moreover, the influence of flow rate change on the internal flow in mixed-flow pump was analyzed. The research results showed that the experimental repeatability of external characteristic was preferable and the result of experiment was reliable. The PIV experiment results showed that the distribution of velocity vector, velocity counter and vortex structure in the mixed-flow pump were greatly affected by the changing of the flow rate conditions. The velocity distribution of impeller inlet was consistent under three flow condition and the incoming flow from impeller inlet was along the axis direction. The velocity of impeller inlet increases with the flow rate increasing and the maximum speed can reach to 7.49 m/s. The velocity gradient of high speed zone from hub to rim was higher and the center of the distribution of contoured velocity was on the upper left corner which was decreasing to around continually. A high velocity area appeared vertically near the impeller under different flow rate conditions during the PIV experiment and the velocity of the fluids increased from the hub to the rim which was caused by the structure of the impeller blade. When the rotating speed was constant, the circumferential velocity of the blade near the rim was much bigger which had a great impact on the fluids nearby. The velocity distribution of gap flow field between impeller and guide vane was disordered which was affected by the rotor-stator interaction when the mixed pump operated. The anticlockwise vortex was formed at the inlet edge of guide vane near the hub and the fluid flowing from the impeller outlet was induced to the blade edge. With the increase in flow rate, the anticlockwise vortex tended to be smaller and the internal flow tended to be steady. Under the large flow rate condition, the maximum velocity of fluids almost reached 4.21 m/s in the middle of the axial clearance between the impeller and guide vanes. The flow field near the guide vane inlet was further influenced by the rotor-stator interaction and then the vortex structure was formed obviously which caused the flow passage congestion. Also, the fluids were structured by the end wall and the flow passages so as to the high velocity zones appeared near the end wall, and the velocity of fluids varied from 3.29 m/s to 3.95 m/s. At the same time, the velocity distribution of the fluids in the circumferential direction that flowed from the impeller also showed the movement axially and obliquely.The large scale vortex structure was formed at the guide vane inlet because of the effect of circular volute chamber. With the increase in flow rate, the high speed zone on edge of the guide vane moved to the downstream, the vortex structures at the guide vane inlet and outlet gradually disappeared while the flow losses decreased. The research results provided reference for revealing the internal flow characteristics of mixed flow pump. Moreover, the analysis of the internal flow fields could optimize the design of impeller of mixed flow pump.