The back-swept double blades sewage pump studied in the paper belongs to the new high efficiency non clogging pump. It has the self-cleaning ability and can effectively solve the problem of fiber winding and congestion. This research was taken on probing the internal flow pattern of relative velocity flow field in the back-swept double blades sewage pump, of which the specific speed was 70. The main design parameters of the pump showed as follows: design flow rateQdes=17 m3/h, headH=9 m, rotation speedn=1 450 r/min. Performance test was done to get the performance parameters curves and results showed the highest efficiency is 61.9% whenQ=21.1 m3/h, corresponding to H=8.2 m. Then PIV test was done and the field distribution for relative velocity flow in the impeller was got. The test PIV system was the US TSI company's commercial PIV system, including: YAG200-NWL type pulse laser; 610035-type synchronizer; 630059POWERVIEW 4MP type cross-frame CCD camera; embedded Tecplot software for image acquisition and data analysis systems Insight 3G; 610015-SOL type light arms and light sheet lens group. External trigger synchronization system comprising: a shaft encoders, flexible couplings, synchronous trigger controller and optical fiber transmission converter. By analyzing the distribution of relative velocity of the impeller in different flow rate conditions (Q/Qdes=0.4, 0.6, 0.8, 1, 1.2, 1.4), we found the variation of axial vortexes and low-speed zones in the impeller. When the flow rate changes from small to large, low-speed zones decrease, and the axial vortex zones were also reduced. When the flow rate changed fromQ/Qdes=0.4 toQ/Qdes=0.6 which means the test the pump was at low flow rate conditions, there were large low-speed regions, axial vortex zones, and the flow field was very unstable, which meaned large hydraulic losses. These axial vortices scattered pressure sides of blades near the inlet, and spreaded to the back of the blade. When the flow rate changes from Q/Qdes=0.6 to the Q/Qdes=1.4, the low speed area gradually reduced. Overall, whenQ/Qdes=0.6 and 0.8, there were low-speed zones and axial vortexes opposite to rotation directions of impeller in the middle zone of channels nearby the pressure surface of the blades, and with the increase of flow rate, low-speed zones and axial vortexes decreases. To explain the phenomenon, the theory of limited number blades in centrifugal pump inner flow was introduced, which considered the relative speed of liquid in rotational impeller as the composition of axial vortex movement and fixed tubular flow. It revealed the fundamental reason for the existence and development of the low-speed zones and vortexes. Meanwhile, we analyzed the relative velocity distribution of different relative phase position between the impeller and volute whenQ/Qdes=0.6, and studied the effect of interference between the impeller and volute on the axial vortexes. It could be known that when the axial vortexes flow through the volute, the vortexes shift to the downstream of the channels. The research results have an important reference value for the further research of the internal flow pattern of protrusive type twisted blades sewage pump.%以一台比转速为70的前伸式扭曲双叶片污水泵为研究对象,采用PIV(particle image velocimetry)技术对双叶片污水泵进行内部流场测量,分析了该泵在不同流量工况下(Q/Qdes=0.4、0.6、0.8、1、1.2、1.4)叶轮内部流场的相对速度分布,研究了轴向旋涡和低速区随流量变化的形态特性,发现在流道中部靠近叶片工作面上存在低速区及与叶轮旋转方向相反的轴向旋涡,且随着流量的增大,低速区与轴向旋涡逐渐减小;引入少叶片数离心泵内部流动理论,揭示了低速区和轴向旋涡存在和发展的内在机理.分析了在流量Q/Qdes=0.6时叶轮和蜗壳不同相对位置的相对速度场分布,研究了叶轮和蜗壳之间动静干涉作用对轴向旋涡的影响,发现当轴向旋涡经过蜗壳隔舌时,其与叶轮之间的干涉作用使得轴向旋涡向下游偏移.研究结果对前伸式扭曲双叶片污水泵的内部流动规律研究具有重要参考价值.
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