Experimental investigation of vortex-ring cavitation

Abstract

Vortex-ring cavitation occurs when the pressure inside a torus-shaped core of a vortex ring falls below the vapor pressure of the ambient liquid. By generating a vapor bubble in a rigid tube, a toroidal cavity can be produced outside the tube. The pulsation and propagation behaviors of vortex-ring cavitation are studied using a high-speed video camera and a hydrophone. The experimental results show that the cavity continues to oscillate with a period that depends heavily on the maximal cross-section radius of the cavity and circulation of the vortex flow, under the influence of the surrounding vortex flow field. It is also shown that the cross-radial oscillation of the toroidal cavity can be measured both by a high-speed camera and hydrophone. Moreover, three different methods for estimating the circulation are compared to propose an accurate model of toroidal cavity oscillation. The phenomenon of a toroidal cavity impinging on a fixed wall is also investigated.

目的

研究涡环空化产生的环状空泡的振荡周期及其冲 击壁面溃灭的动态过程。

创新点

1. 通过实验方法,比较几种不同的速度环量计算 模型在环状空泡振荡控制方程中的适用性。2. 通 过声学方法,得到环状空泡在撞击壁面溃灭过程 中的频谱特征。

方法

1. 通过管内空泡膨胀产生高速射流;高速射流在 管口处形成涡环并发生涡环空化。2. 基于高速摄 像进行流体分析。

结论

1. 在管内空泡溃灭后,环状空泡以恒定速度沿管 的轴向运动,且其振荡周期几乎保持不变。2. 环 状空泡的振荡周期基本上满足规律: τ~ R0(ρ /ΔP)^0.5[ln(8/ε)]^0.5。3. 在空泡振荡的最小直径 为特征直径;根据空心涡核模型,可以计算得到 最接近实验结果的速度环量值。4. 当空泡冲击壁 面时,空泡的环向直径将变大。5. 环向直径的最 大扩 张比α与其截面直径与环向直径的比ε相关: α~ε ^0.25。