Numerical Investigations on Water-entry Cavity of Half Hydrophobic-half Hydrophilic Sphere

The water entry of a solid sphere impacting on a liquid surface has challenged researchers for centuries and remains of interest to the researchers today. A simulation study of the water entry cavity of half hydrophobic-half hydrophilic sphere is performed. Particular attention is given to the simulation method based on solving the Navier-Stokes equations coupled with VOF model and CSF model. The numerical results are in agreement with the experimental results, thus validating the suitability of the numerical approach to simulate the water entry of sphere under different wetting conditions. Based on this method, the development of cavity created by the half hydrophilic-half hydrophobic sphere is investigated. Results show that the water entry of half hydrophobic-half hydrophilic sphere creates an asymmetric cavity and “cardioid” splash, which causes the sphere to travel laterally from the hydrophobic side to the hydrophilic side. Further investigations show that the fluid film presents during initial stage of impact, and on the half hydrophobic sphere, the fluid film detaches from the sphere to lead to cavity formation; on the half hydrophilic sphere, the fluid film moves up on the sphere surface and gathers at the vertex of the sphere, forming a wedge flow. The wedge flow moves and finally impacts on the opposite side of the cavity so as to cause “cardioid” splash. In addition, the total hydrodynamic force coefficient is investigated as a result of the forces acting on the sphere during water entry dictated by the cavity formation. © 2017, Editorial Board of Acta Armamentarii. All right reserved.