轴流泵叶轮端壁区流动特性数值模拟

Numerical Simulation of Flow Field Characteristics in Tip Clearance Region of Axial-flow Impeller

轴流泵端壁区流动对流场结构、能量传输、水力效率等有着重要的影响。基于CFD技术和高质量结构化网格,对不同叶顶间隙的轴流泵方案进行了全流场数值模拟,探讨了叶顶间隙对端壁区轴面速度、环量等流动参数的影响规律,分析了叶顶泄漏涡的产生机理及其结构,并与高速摄影试验进行了对比。研究结果表明,端壁区叶顶间隙导致进口轴面速度非均匀分布和轮缘侧二次回流;叶轮出口的端壁间隙区轴面流动减弱,且叶顶间隙越大,轴面速度下降幅度越大;叶顶间隙附近的二次回流区使叶轮进口产生环量,当叶顶间隙增大至2 mm时,约50%的流动区域受到间隙的影响而产生预旋;端壁区叶顶泄漏涡的数值模拟运动轨迹及结构与试验一致,在小流量工况下,泄漏涡强度增强,且干扰流场范围扩大。

The flow in end wall region of axial-flow impeller has an important impact on flow structure, energy transfer and hydraulic efficiency. The hydraulic axial-flow pump models with different tip clearance sizes were simulated based on CFD technology and high-quality structured grid. The influence of tip clearance on the meridional velocity and circulation distributions in impeller inlet and outlet were discussed, and the leakage vortex generation mechanism and its structure were analyzed as well. The numerical results were compared with high-speed photography experimental results. The investigation results showed that tip clearance led to non-uniform meridional velocity distribution in impeller inlet and secondary flow in end wall region occurred, meridional velocity near tip clearance in impeller outlet decreased, and the bigger the gap was, the bigger decline of meridional velocity would be. The secondary reeirculation near the wheel led to circulation of impeller inlet, when the gap increased to 2 mm, about 50% of the whole flow passage appeared circulation which impacted by the tip leakage vortex. The trajectory and structure of tip leakage vortex in the numerical simulation showed agreement with the experimental results. Under the small flow rate conditions, the leakage vortex strength and the influence regional scale were increased.