考虑表面润湿性的球体垂直入水空泡及流体动力数值研究（英文）

Numerical Simulation of Cavity and Hydrodynamic Force of the Sphere Water Entry in Consideration of Surface Wettability

本文通过数值仿真方法对球体垂直入水过程产生的入水空泡形态及流体动力特性开展了研究,重点分析了表面润湿性对球体入水空泡发展过程、运动轨迹、速度、加速度及流体动力的影响.文中数值方法基于Navier-Stokes方程,采用VOF模型捕获相界面,并通过CSF方法引入表面张力及表面接触角.结果表明,数值结果与文献实验结果吻合良好,验证了数值方法的有效性;由于亲水性球体入水后不产生空泡,压差阻力较小,因此下落速度更快,而疏水性球体下落较缓慢;当入水空泡掐断时,将对球体产生短暂的冲击作用,使球体运动速度发生突变;在入水过程初始阶段,球体表面上的液体薄层运动是导致入水空泡形成的关键因素:对于亲水性球体,流体薄层沿球体表面向上运动并在球体顶点汇聚,此时不产生入水空泡;对于疏水性球体,液体薄层与球体分离,形成入水空泡.

Based on the numerical simulation method,this paper carried out the numerical research of vertical water entry of spheres,and focused on the influence of the surface wettability on the developing process of the water entry cavity.The results of cavity formation,trajectories,velocities,accelerations,and hydrodynamic force acting on the sphere are presented.The numerical method is based on Naiver-Stokes equations,by using the VOF model the interface is captured,and surface wettability was introduced through the CSF method.The numerical results are directly compared with the experimental results from the literature,which verifies the accuracy of the numerical method.Results show that surface wettability has a significant effect on the water entry cavity,especially in relatively low speed.The hydrophilic sphere falls faster and meets smaller drag while the hydrophobic sphere falls more slowly and brief mutation will happen in the motion when cavity is pinched off.In the early stage of water entry,the formation of fluid film movements on the surface of the sphere is the critical factor that leads to the formation of water entry cavity.For hydrophilic sphere,the fluid film moves upward along the sphere surface and forms up sputtering flow in the sphere vertex positions and does not produce the water cavity;for hydrophobic sphere,the fluid film detaches from sphere surface,which leads to air entrainment and the formation of water entry cavity.