表面润湿性对球体入水空泡形态的影响研究

Effect of Surface Wettability on Cavitation of Sphere during Its Water Entry

基于Navier-Stokes方程,采用流体体积法多相流模型,并引入动网格技术,对不同表面润湿性球体的垂直入水问题开展了数值模拟研究。将球体垂直入水空泡形态的数值结果与实验结果进行对比,验证了数值结果的正确性。对不同润湿性球体的垂直入水空泡形态的研究结果表明,球体入水空泡形态主要有4种:完全无空泡、深闭合空泡、面闭合空泡以及类面闭合空泡。入水初期形成的液体薄层是影响随后产生空泡形态的关键因素。进一步分析表明,生成不同空泡形态的临界速度与球体的表面润湿性有密切关系,建立了描述入水空泡生成的临界速度与表面接触角关系的经验公式。

The problem of water entry of a solid sphere has challenged researchers for centuries and remains of interest to the researchers today,but how the surface condition affect the cavitation during a water entry of sphere has not been studied well. The problem of water entry of a solid sphere is investigated numerically simulated based on the Navier-Stokes equations and volume of fluid method. The numerical results show good agreement with the experimental data. Numerical results with different surface wettabilities and impact speeds are presented. The results show that the condition to create an air cavity is that the impact speed must be strictly above a critical velocity,and the critical velocity is discovered to be dependent on the wetting contact angle of sphere. That means the air entrainment is best inhibited by hydrophilic surfaces,hydrophobic spheres like making a big cavity. Four distinct cavitations are observed at different water entry velocities and contact angles： non-cavitation,deep-seal cavitation,surface-seal cavitation and surface-like cavitation. The simulation results are analyzed,and an empirical theory about the relationship between critical velocity and contact angle is presented.