Modeling of surf zone processes on a natural beach using Reynolds‐Averaged Navier‐Stokes equations

Abstract

The use of an advanced volume of fluid (VOF)‐type model (COBRAS‐UC), based on the Reynolds‐Averaged Navier‐Stokes (RANS) equations, is proposed in this work with the aim of improving the current state of understanding of surf zone processes on natural beaches. Previous studies have suggested that it is important to consider contributions from terms traditionally neglected when assuming a uniform velocity and pressure distribution and a simple turbulence parameterization in surf zone hydrodynamics. In contrast with the Boussinesq and Nonlinear Shallow Water (NSW) equations models, in the RANS models none of the above‐mentioned limiting assumptions is required, since no wave theory is imposed and the initiation of wave breaking is predicted by using an advanced turbulence model. Although the model has been widely validated in the laboratory, there is no previous study, to the best of the authors' knowledge, which addresses the applicability of this model to random waves on natural beaches. Free‐surface elevation and wave‐induced velocity observations, from the SwashX field experiment, are used to validate this model. The model is able to satisfactorily predict the wave evolution and flow characteristics across the surf zone. The model provides a means to obtain high spatial and time resolution information of magnitudes which are difficult or impossible to measure in the field and therefore may contribute to improve our understanding on the physics of surf zone hydrodynamics. Moreover, it is also an excellent tool to obtain useful information of magnitudes involved in different kinds of modeling that require parameterization.