Numerical study on dissipation rates of wave and roller energies under breakers: Closures for rates

Abstract

This study uses computational fluid dynamics (CFD) simulations with the Reynolds stress model to investigate surf-zone hydrodynamics under spilling breakers, focusing on the dissipation rates of wave and roller energies. Two sets of full-scale CFD simulations are performed: one on a planar beach and the other on a barred beach. The flow field is decomposed into wave and roller components based on the vorticity values, from which the energy fluxes are extracted. Based on planar beach simulations, two new closures are proposed to determine the dissipation rates. The novelties of the closures include (i) an evolution equation for the time scale of wave-energy dissipation, and (ii) a roller-property-based time scale for roller-energy dissipation. Barred beach simulations validate the proposed closures. Jointly, these closures enable accurate predictions of the wave and roller energy fluxes in the surf zone under spilling breakers, reducing the normalized root-mean-square error by approximately 70% and 50% for wave and roller energy fluxes, respectively, on planar beaches compared to existing formulations.