Flow Modulation and Wave Impact Reduction by Retreated Crown Walls in Vertical Breakwaters

This study investigates wave-induced flow behaviour around vertical breakwaters with retreated crown wall using numerical simulations. Previous experimental work has shown that moving the crown wall landward can reduce wave forces, moments, and overtopping. However, the associated flow mechanisms near the wall and trunk region have not been examined in detail. In this work, the open-source CFD model REEF3D is used to simulate regular wave interaction for crown wall retreat configuration. The model solves the Reynolds-averaged Navier–Stokes equations, with a level set method for free-surface tracking and a k–ω turbulence closure. The numerical results are first validated against published experimental data to ensure accuracy. The simulations provide detailed information on velocity fields, vortex formation, and flow separation during wave impact and overtopping. The results show that retreating the crown wall modifies the local flow structure, leading to a redistribution of momentum and a reduction in direct wave impact on the wall. These findings help to clarify the hydrodynamic role of retreated crown wall in vertical breakwater design.