不同空泡脱落模式下空化多尺度特性研究

Cloud cavitation is a complex transient multiphase flow phenomenon centered around phase transitions, containing the growth and evolution behavior of bubbles under multiple scales. In this paper, the multiscale cavitating flow on a NACA66 hydrofoil at a cavitation number σ=1.2 and an angle of attack of 8° is studied through a two-way coupling Euler-Lagrange method. The evolution of large-scale cavities under the Euler framework is resolved using the Volume of Fluid (VOF) interface capturing method, while the motion and growth-collapse process of subgrid-scale discrete bubbles are tracked using the Discrete Bubble Model (DBM) in the Lagrangian framework. The results demonstrate that the cloud cavitation flow around the hydrofoil includes four phases: growth and development of attached sheet cavities, formation and evolution upstream of re-entrant jet, detachment and shedding downstream of cloud cavities, and the regrowth of macro-scale bubbles, along with the propulsion of shock waves. The number and size of discrete bubbles change with the periodic evolution of large-scale cavities, primarily distributed in areas of strong turbulent pulsations. During various stages of cavitation development, discrete bubbles are concentrated at the mid-rear part of the hydrofoil. The probability density function of micro-bubble diameters follows a unimodal Gamma distribution, with a dominant size about 50 μm. During the growth stage of attached cavities with lesser turbulence, the micro-bubble number density relative to bubble diameter exhibits a -5/3 power-law characteristic. In stages of higher turbulence, such as the development of re-entrant jets, cloud cavity shedding and collapse, and shock wave propulsion, the micro-bubble number density relative to bubble diameter shows a -2/3 power-law characteristic in smaller size ranges and a -6 power-law characteristic in larger size ranges.