超低比转数离心泵的内部流动及非定常特性

Internal flow and analysis of its unsteady characteristics in centrifugal pump with ultra-low specific-speed

为全面地研究超低比转数离心泵的内部流动和非定常特性,以一台比转数ns=25的超低比转数离心泵为研究对象,对其进行三维非定常数值计算,并与试验结果进行对比,进而对内部流场、叶轮上的径向力和蜗壳各断面的压力脉动进行分析.研究结果表明:在不同流量工况下,叶轮流道内存在数量不等、大小不一的旋涡;靠近隔舌的2个相邻流道内,在叶轮出口边工作面的位置存在高流速区域,随着流量的增大,此处高流速区域逐渐消失;在大流量工况下,低速区面积逐渐减小,旋涡区的范围和数量逐渐减少,叶轮内相对速度分布逐渐变均匀;叶轮上的径向力大小和方向时刻变化,呈现六角星型分布,径向力脉动的主要激励频率均为叶频及其整数倍频;蜗壳各断面内压力脉动峰值随着断面变化逐渐增大,蜗壳各断面内压力脉动的主要激励频率均为叶频及其整数倍频,说明叶轮出口与蜗壳的耦合作用是蜗壳内压力脉动的主要影响因素.研究结果可为超低比转数离心泵的水力优化设计和合理运行区间的选择提供一定参考.

In order to explore internal flow and its unsteady characteristics in ultra-low specific-speed centrifugal pumps more comprehensively,an ultra-low specific-speed centrifugal pump with a specific-speed n s=25 was chosen as a study object.Then numerical simulations of the unsteady three-dimensional fluid flow in the pump were carried out.Finally,the internal flow field,radial thrust on the impeller and the pressure fluctuation of fluid in each section of the volute were analyzed.The results show that there appears vortices in various sizes and numbers in flow channels of the impeller under different flow conditions.A high velocity zone is found in two adjacent channels near the tongue,however,the zone disappears gradually with the increase of flow rate.Under high flow rate conditions,the area of the low velocity zone decreases gradually,the size and number of vortices reduce steadily,and the rela-tive velocity distribution in the impeller becomes uniform gradually.The orientation and magnitude of radial thrust on the impeller vary constantly,showing a hexagram pattern.The amplitude of radial thrust decreases gradually with increasing flow rate,but its main excitation frequencies are all the blade passing frequency or its integer multiples.The peak pressure fluctuation in each section of the volute decreases along the flow path and the main excitation frequencies are all the blade passing frequency or its integer multiples.This fact suggests that the impeller-volute interaction is one major factor influencing pressure fluctuation in the volute.These results have provided useful reference for optimum design of the ultra-low specific-speed centrifugal pump and selection of its feasible operating flow rate range.