绕水翼超空化流发展及其旋涡特性的实验研究

为深入了解超空化流场结构特性,利用数字粒子图像测速(DPIV)和高速全流场显示技术,观测了绕hydronautics水翼的超空化流动涡量场。采用空化流场中的空化泡作为示踪粒子来显示流动结构。结果表明:在超空化的不同发展阶段,流动涡量场呈现不同的分布特征:随着空化数的降低,上下涡带逐渐靠拢,并向后延伸、拉直;下涡带随空化区域内汽相和水汽混合相分布的不同而发生明显变化:空穴形成阶段的下涡带基本稳定;在两相共存阶段,汽相和水汽混合相的频繁转换使得下涡带的起始位置和形状发生剧烈的变化;而在超空化完全发展阶段,下涡带又趋于稳定,且起始位置移至水翼后部。在整个超空化阶段,汽相和水汽混合相之间存在着较大的速度梯度;与来流方向相比,垂直于来流方向的速度脉动要大得多。

Experimental study on the development and vortex characteristics of supercavitating flows around a hydrofoil

To understand the characteristics of supercavitating flows,the vorticity distribution in the flow around a hydrofoil was measured by means of a digital particle image velocimetry(DPIV) system,accompanied with a high-speed video camera to visualize the flow structures at different cavitation numbers.The cavitation bubbles inside the cavitating fields are used as the tracer particles. The results show that the vorticity distribution in the whole flow field depends on the development of super-cavitation: With reducing the cavitation number,the upper and lower vortex bands approach with each other and extend downstream with strait manner.The lower vortex band changes significantly as the distribution of the vapor phase and water-vapor phase varies.The following phenomenon was observed.It behaves steady during the cavitation formation stage;the lower vortex band fluctuates violently at the two-phase coexist stage due to frequent interchanges between the two phases;it becomes smooth and moves to the downstream at the fully developed stage.Finally,it was found that larger velocity gradient exists between the vapor phase and the water-vapor phase at the whole supercavitation stage,and the velocity fluctuating in the vertical direction behaves more violently than that in the flowing direction.