Comparison of Turbulent Flows and Suspended Sediment Particle Motions Simulated around a Submerged Breakwater Using RANS and LES

Abstract

Beach erosion is a serious problem that can be aggravated by human-made structures, and the modeling of breaking waves near the coast and around coastal structures can be used to determine their impact. In this study, OpenFoam was employed to simulate turbulent flows around a submerged breakwater (SBW) to compare the performance of two turbulence modeling schemes-RANS and LES. We coupled a Lagrangian sediment particle module with OpenFoam to examine the turbulence caused by breaking waves. The numerical setup for the simulations was based on bathymetry measurements made at Hujeong Beach in South Korea. The results show that the wave heights simulated by LES were higher than those simulated by RANS in the front and lee areas of the SBW, and they were lower at the top of the SBW. This indicates that a larger amount of wave energy was conserved after passing over the SBW according to LES. These results were also confirmed via the obtained turbulent kinetic energy (TKE). When using LES, TKE increased in the lee area, where the waves broke after passing over the SBW. In case of RANS, however, TKE was not successfully conserved; it significantly decreased in the lee area. Lagrangian sediment motions show that, when using LES, a strong eddy formed, which entrained and dispersed the sediments into the water column. In the case of RANS, however, no evidence of such turbulent eddy formation was found, which confirms the better performance of LES for resolving turbulence.