水翼叶顶间隙漩涡空化流动特性研究

Investigation of vortical cavitating flows in tip leakage region of a hydrofoil

采用试验的方法研究了不同空化数下水翼叶顶间隙区域漩涡空化流动的发展变化。试验在闭式空化水洞中进行,采用高速全流场显示技术对空化流场进行观测,并采用图像处理技术对试验结果进行处理,提出空化涡模型,阐述了涡空化的发展规律。研究结果表明:随着空化数的降低,叶顶间隙漩涡空化的发展主要经历如下三个阶段:(I)泄露涡内部空化初生阶段:在水翼中部附近产生游离状空化,向下游运动并迅速溃灭消失。(II)叶顶间隙内部附着空化发展阶段:涡空化逐渐发展并向水翼尾缘延伸,空化涡带呈螺旋状非轴对称旋转;叶顶位置压力面中部附近开始出现片状附着型空化,并体现出强烈的非定常特性。(III)射流剪切层内部空化形成阶段:涡空化延伸至水翼下游;叶顶附着空化充分发展,充满间隙并形成射流剪切层空化,和空化涡带共同形成三角状空化结构。

Experimental investigations of unsteady cavitating flows in a hydrofoil tip leakage region are con-ducted to highlight the development of cavitation with various cavitation numbers. The experiments were taken in a closed cavitation tunnel, during which high speed camera was used to capture the cavitation patterns. Image processing was also used to get further analysis. Besides, cavitating vortex model is proposed to de-scribe the development of vortex cavitation. Based on the results, three stages can be defined as the de-crease of cavitation number. In the first stage, called the inception of tip leakage vortex cavitation, a rapid onset-growth-collapse process of the vortex cavitation can be observed near the middle and rear parts of the hydrofoil. In the second stage, called the development of attached leakage cavitation, aforementioned vortex cavitation develops gradually with non-axisymmetric and twists rotation, and attached sheet cavitation inside the gap with strong unsteadiness can be observed neat the middle part of the hydrofoil. In the last stage, called formation and development of jet shear layer cavitation, vortex cavitation stretches towards downstream, and aforementioned attached cavitation develops beyond the gap and combines with the vortex cavitation, to form the triangle cavitating region.