云状空化非定常脱落机理的数值与实验研究

NUMERICAL AND EXPERIMENTAL STUDIES ON UNSTEADY SHEDDING MECHANISMS OF CLOUD CAVITATION

结合数值计算和实验技术研究了云状空化的非定常脱落机理.实验采用高速录像技术观察了绕Clark-y型水翼云状空化形态随时间的变化.数值计算采用了汽-液两相的当地均相流模型,湍流封闭采用了一种修正的RNG k-ε方程,利用商业软件的二次开发技术,引入了一种与空化区域水汽相密度相关的系数,对湍流模型进行了修正.计算和实验结果均表明:云状空化尾部存在着准周期性的涡状空化团的脱落;局部压强的增加是引起空穴断裂进而脱落的直接原因;压强升高是由于近壁处的反向射流引起的;空穴尾部的大规模的旋涡运动引起的近壁处的逆压梯度是引起反向射流的主要原因.

The unsteady characterics of cloud cavitating flow around a hydrofoil are investigated by the experimental and numerical methods. Experiments on a hydrofoils are carried out in a rectangular test section of a cavitation tunnel. A high-speed video camera is used to visualize the unsteady flow structures. The caculations are conducted on the two-dimensional hydrofoil section, based on a single-fluid model of the cavitation： the liquid/vapor mixture is considered as a homogeneous fluid whose compsition is regulated by mass tranfer equation. The RNG k-ε turbulence model with modified eddy viscosity coefficient is used in the computation, and the coefficient is related to the vapor and liquid densities in cavitated regions for simulating the cavitating flow. The experimental and numerical results show the unsteady features of the peridical cloud cavity departure; the increasing of a local pressure is a main factor to induce ruture of a cloud cavity; an interaction between the re-entrant jet and the cavity interface in the closure region can lead to the increasing of the local pressure; the adverse pressure gradient is mainly responsible for the generation of the re-entrant jet.