轴流泵运行工况和叶顶间隙对叶顶泄漏涡轨迹的影响

采用SST k-ω湍流模型模拟和旋涡强度方法,对某一轴流泵模型泵叶轮叶顶区流场和叶顶泄漏涡轨迹进行了数值计算,分析了运行工况和叶顶间隙两个因素对轴流泵叶顶泄漏涡运动轨迹的影响.数值模拟结果表明,随着流量增大,轴流泵叶顶泄漏涡的涡核轨迹起点由叶尖向叶片翼型中部逐渐移动.随着流量的增大,叶片流道内的流动方向发生偏移,叶顶泄漏涡在主流的卷吸下,运动轨迹随之变化,涡轨迹线的斜率受叶轮内主流的影响而变大.随着叶顶间隙增大,泄漏涡的卷吸程度逐渐增强,影响范围增大,涡核的起点由叶片前缘逐渐向后缘移动,且涡核的压力逐渐降低,因此在大间隙时涡带更易出现空化现象.当叶顶间隙达到1.5 mm时,轴流泵在0.9Qd工况附近出现驼峰现象,说明叶顶泄漏涡对驼峰区不稳定流场具有重要的影响.

Influence of operational condition and tip clearance size on trajectory of tip leakage vortex

Based on the SST k-ω turbulence model and vortex intensity method,the flow through the impeller tip and tip leakage vortex trajectory in a model axial-flow pump were simulated numerically.The influence of operational condition and tip clearance size on the trajectory was analyzed.It is shown that the starting point of leakage vortex core moves to the middle portion of blade from the blade leading edge gradually with increasing flow rate.The relative flow direction in the impeller passage is deflected and the trajectory of tip leakage vortex is altered accordingly under the entrainment induced by the primary flow with increasing flow rate as well.Note that the slope of the vortex core trajectory also gets enlarged by the primary flow.The rollup of leakage vortex is enhanced and the affected region is expanded,the starting point of the vortex also moves from the leading edge to the trailing edge,and the static pressure in the vortex core is decreased gradually,causing a risk of cavitation with increasing tip clearance size.A positive head curve appears at around 0.9 times the design flow rate under a tip clearance as large as 1.5 mm,suggesting the tip leakage vortex can influence the instability of head curve significantly.