Numerical modeling of the hydrodynamics of standing wave and scouring in front of impermeable breakwaters with different steepnesses

•We model standing wave hydrodynamics in front of different breakwater steepnesses.•Steady streaming system and scouring process are well simulated.•Calculation of bottom shear stress is required to produce a physical bed profile.•The breakwaters with gentler steepness dissipate more wave energy.•Scouring does not occur in front of a very gentle breakwater.

The aim of this paper is to numerically study the effects of breakwater steepness on the hydrodynamics of standing wave and scouring process in front of impermeable breakwaters. A two-dimensional hydrodynamics model based on the Reynolds Averaged Navier–Stokes (RANS) equations and the Volume of Fluid (VOF) method was developed and then combined with an empirical sediment transport model. Comparisons with an analytical solution and experimental data showed the present model is very accurate in predicting the near bottom velocity and capable of simulating the scour/deposition patterns consistent with experimental data. It was found that the additional terms of bottom shear stress in the momentum equations are necessary to produce a physical scouring pattern. Different breakwater steepnesses produce different characteristics of standing wave, the steady streaming system, and scouring pattern in front of the breakwaters, which also affects the correlations between them. An additional analysis of the turbulence field parameters and the sediment transport rate was also performed. All these important information will be presented in details in this paper and can be worthwhile for designing the breakwater in coastal areas.