射流式离心泵性能及内部流动特性

Performance and internal flow characteristics of jet centrifugal pump

为研究射流式离心泵内流动机理,以JET750G1型射流式离心泵为研究对象,搭建试验测试系统,分别对不同安装高度下射流式离心泵的空化及能量特性进行试验研究;基于k-ω湍流模型和Zwart-Gerber-Belamri空化模型,对0mm安装高度下泵各工况点内部流动进行数值模拟.试验结果表明:当流量增大到一定程度之后,扬程-流量、功率-流量、效率-流量曲线均急剧下降;随着安装高度的增大,陡降起始点向小流量工况偏移.数值计算结果表明:扬程、功率、效率的数值模拟结果与试验值基本吻合,数值模拟性能陡降起始流量比试验值大0.5m^3/h;射流式离心泵由于其面积比值较小,射流剪切层被迅速排挤到喉管壁面,泵内最低压力点出现在喉管内喷嘴稍后处,空化最早发生在该处;随着流量的增大,空化区域急剧向叶轮进口扩展,性能陡降起始点正好是泵内初生空化流量点,射流式离心泵的空化性能取决于其射流器的空化性能;射流器能提升离心泵扬程和自吸性能,但射流器内高速回流及强剪切流动,导致其效率及空化性能大幅下降.

Experiments on suction and hydraulic characteristics were performed at different installation heights in a fluid flow testing system built to investigate self-priming mechanisms in jet centrifugal self-priming pumps in term of the type JET750G1 jet centrifugal pump.Also,a series of numerical simulations of cavitating flows in the pump were carried out based on the K-ω turbulence model and Zwart-Gerber-Belamri cavitation model at zero installation height.The experimental results show that the head,shaft-power and efficiency curves drop sharply when the flow rate reaches a certain value.As the installation height increases,however,the flow rate at the point for performance starting to drop steeply gets lower.The numerical results exhibit that the predicted head,shaft-power and efficiency are basically consistent with experimental values,and the estimated flow rate for performance starting to drop steeply is 0.5 m^3 /h larger than the experimental value.Because of a smaller area ratio in the jet nozzle,the primed fluid shear layer is rapidly dragged to the wall of the throat,and the lowest pressure appears just after the throat outlet where cavitation begins to occur.As the flow rate increases,the cavi-tion extends rapidly to the eye of impeller.The flow rate at the point for performance starting to drop steeply is exactly the flow rate for cavitation inception in the pump.Thus,the suction performance of a jet centrifugal pump depends on the performance of ejector.An ejector can improve the head and self-priming performance of a centrifugal pump,but the high velocity reverse flow and strong shear flow in the ejector will lead to a significant drop in pump efficiency and suction performance.