球体垂直入水过程流体动力数值研究

Numerical investigations of hydrodynamic force acting on sphere during water entry

采用VOF(Volume of Fluid)多相流模型耦合CSF(The Continuum Surface Force Model)模型,对亲水性及疏水性球体垂直入水过程进行了数值研究。将数值结果与文献实验结果对比,验证了数值方法的可靠性。在此基础上,开展亲水性及疏水性球体垂直入水数值研究。结果表明,亲水性球体在较低入水速度下不产生入水空泡,而疏水性球体产生较大入水空泡,空泡在自由液面以下某一位置闭合形成"沙漏状"空泡形态。入水初期在球体表面形成液体薄层运动是导致空泡形成与否的关键因素,对于亲水性球体,液体薄层沿球体表面向上运动并在球体顶点位置汇聚形成向上的溅射流,不产生入水空泡;对于疏水球体,液体薄层在球体赤道位置附近与球体表面分离,导致空气进入,形成入水空泡。通过球体入水过程运动轨迹、速度、加速度,分析了表面润湿性及密度对球体入水过程运动参数的影响。最后,分析了球体入水过程中受到的总流体动力,发现亲水性球体在垂直入水过程中下落速度更快,守到更小的总流体动力,表明其受到更小的阻力。

The water entry of hydrophilic and hydrophobic spheres with different density was investigated by numerical simulations. During the simulation, the Reynolds-Averaged-Navier-Stokes equations were solved with the VOF （volume of fluid） method coupled with the CSF method （The Continuum Surface Force Model）. Numerical results with different wetting properties and different densities were presented, and directly compared with the experimental results from published literature,showing a good agreement with the experimental results, demonstrating that the simulation methodology is trustable in handling such a problem. Based on this methodology, the water entry cavity created by sphere was investigated. The fluid film developing during the early stage of water entry was shown, which is helpful for illustrating the mechanism of water entry cavity formation. The effect of wetting properties on the sphere ’ s trajectory,velocity, acceleration was discussed. Finally, the total hydrodynamic forces acting on the sphere during water entry were investigated,showing that the hydrodynamic force acting on hydrophilic sphere was much smaller than hydrophobic sphere, and the hydrophilic sphere descend more quickly during water entry, indicating a much smaller drag force.