A fully 3D simulation of fluid-structure interaction with dynamic wetting and contact angle hysteresis

Abstract

In this paper, we propose a three-dimensional diffuse-interface immersed-boundary (3D DIIB) method for the simulations of fluid-structure interaction (FSI) with dynamic wetting, complex geometry and contact angle hysteresis. In particular, the movement of rigid solid objects is allowed to have six degrees of freedom. In the method, the complex solid boundaries are represented by a set of Lagrangian patches that cover the whole surface of the solid objects, while the flows are solved on a staggered Cartesian grid. The couplings between the object movement and surrounding fluid flows are performed using an immersed boundary method. A simple model of contact angle hysteresis is used to ensure pinned contact lines if local contact angle is within the window of contact angle hysteresis. To relieve the stress singularity at moving contact lines, a characteristic moving contact line model [1] is adopted at 3D curved solid surfaces, after the geometrical information of interface is constructed in the vicinity of the contact line. For 3D simulations of FSI with dynamic wetting, it is crucial but difficult to estimate capillary force, of which the process consists of locating the moving contact line on complex solid surfaces, discretizing it into line segment, and determining the local tangent to the interface at the contact lines. Special consideration is given to the modeling of the capillary force and associated torque, in order to have accurate approximations. The performance of the 3D DIIB method is systematically examined through a series of numerical experiments, of which the results are either verified against theoretical predictions or compared with experimental data. Finally, we simulate the collision process of raindrops with 3D mosquito body, to show the potential of the 3D DIIB method in practical applications.