轴流泵叶顶间隙空化流可视化实验研究

Visualization Research on Cavitating Flow in Tip Clearance of Axial-Flow Pump

运用高速数码摄像系统对比转速为700的轴流泵在最优工况流量下不同空化程度时的叶顶间隙内空化流动进行拍摄实验,捕捉到空化发生位置和空泡团形态随空化程度变化的演变过程。实验结果表明:叶顶间隙内空化发生的初始位置位于叶顶翼型头部,空泡团为沿叶片工作面向背面旋转的旋涡空化,旋转轴和圆周方向基本一致;随着泵汽蚀余量的降低,空化发生位置和空泡团与叶顶翼型粘连的区域均呈由叶顶翼型头部向尾部延伸发展的趋势;当泵发生汽蚀时,空化发生位置覆盖整个叶顶翼型,间隙空泡团和叶片背面空泡团相掺混,对叶轮流道内液相主流产生强烈干扰,导致泵能量性能急剧下降。研究结果为轴流泵叶顶间隙内空化发生及发展过程的理论研究提供了有效参考。

With the change of NPSH, the cavitating flow in tip clearance of axial-flow pump with specific speed of 700 at the flow rate of best efficiency point were shot by the high speed digital camera. The evolution of cavitation region and the form of cavitation bubbles cluster were tracked. The experimental results show that the initial cavitation region is located in the leading edge of tip airfoil. The type of cavitation is vortex cavitation rotating from blade pressure surface to suction surface, its rotation axis direction is the same as circumferential direction. With the decrease of NPSH, the cavitation region at the tip airfoil moves gradually from the leading edge to the trailing edge and the adhesion between the cavitaion bubbles and the tip airfoil indicates the same moving trend. As the pump being cavitation, the cavitation region at the tip airfoil covers the whole airfoil and the admixture of cavitation bubbles emerging at the tip airfoil and the blade suction surface disturbs the main flow in the impeller channel and deteriorates the pump performance rapidly. The experimental results provide an effective reference for the cavitation region and development process in tip clearance of axial-flow pump.