Abstract
A numerical simulation to investigate the water entry of half-half sphere which is hydrophobic on one hemisphere and hydrophilic on the other is performed. Particular attention is given to the simulation method based on solving the Navier-Stokes equations coupled with VOF (volume of fluid) method and CSF (continuum surface force) method. Numerical results predicted experimental results, validating the suitability of the numerical approach to simulate the water entry problem of sphere under different wetting conditions. Numerical results show that the water entry of the half-half sphere creates an asymmetric cavity and “cardioid” splash, causing the sphere to travel laterally from the hydrophobic side to the hydrophilic side. Further investigations show that the density ratio and mismatch of asymmetric in wetting condition affect the trajectory, velocity, and acceleration of the half-half sphere during water entry. 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.
Highlights
The water entry problem of a solid object impacting on a liquid surface has challenged researchers for centuries
The time-dependent governing equations were discretized by using the finite volume method; the SIMPLE algorithm was used for coupling between pressure and velocity with a green-gauss cell based gradient evaluation option to solve Reynolds-Averaged Navier-Stokes (RANS)
The numerical simulation results reveal that, by a change in the surface wetting conditions, it is possible to change the water entry behavior when a sphere impacts onto a free liquid surface
Summary
The water entry problem of a solid object impacting on a liquid surface has challenged researchers for centuries. The first systematic study of water entry problem, such as splashes and cavity formation, was published more than a century ago by Worthington [5], who used single-flash photography to investigate the process of solid objects impacting on liquid surfaces. He observed that the water entry of spheres coated with soot formed a distinct subsurface cavity whereas an already wetted sphere did not. The ultimate result presented is that the asymmetrical cavity formation can be produced by dropping a half-half sphere that is hydrophobic on the hemisphere side and hydrophilic on the other This phenomenon is the main focus of this paper. The trajectories, velocities, accelerations of the sphere, and the forces acting on it during water entry are investigated
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