Lagrangian two-phase flow modeling of scour in front of vertical breakwater

Abstract

A Lagrangian particle-based two-phase flow model is developed to simulate the scouring process induced by standing wave in front of the trunk section of a vertical breakwater. Given the two-dimensional nature of the scouring problem at the trunk of vertical wall, the fluid phase is simulated with two-dimensional Navier–Stokes equations based on weakly compressible smoothed particle hydrodynamics (WCSPH) formulation in conjunction with sub-particle scale (SPS) turbulence closure model. The sediment phase is simulated using the Discrete Element Method (DEM). The effects of interparticle and particle-wall collisions are computed by activating a spring-dashpot system. The WCSPH fluid-phase and DEM sediment-phase are coupled through a weakly one-way coupling procedure using wave orbital velocity. The numerical model is successfully validated against experimental data. The maximum scour depth predicted by WCSPH-DEM model is closely approximate the experimental data. This study, for the first time, demonstrated an extra recirculating sediment transport mechanism in front of the vertical breakwater, similar to steady streaming recirculating cells in the fluid phase, which has a direct impact on the formation of scour hole and maximum scour depth at the breakwater trunk. The scenario modeling conducted in this study show that by increasing the steady streaming velocity, the deposition rate and the depth of scour hole were increased.