Modelling Combined Wave–Current Flows Using a RANS CFD Solver with Emphasis on the Effect of the Turbulent Closure Model

Abstract

The nearshore hydrodynamics and coastal circulation result from the contribution of a variety of phenomena which have complex physical interactions at different scales. Among these interactions, we focus here on the interaction between waves and current. In the present work, the evaluation and analysis of wave–current interactions is made through numerical simulations based on Reynolds averaged Navier–Stokes (RANS) equations, applied to the modelling of the complete flow motion, namely waves and current simultaneously (i.e., without decoupling the two phenomena). The advanced CFD code Code_Saturne [1] is used for this purpose. The code is adapted for the study of waves and current interactions, using the arbitrary Lagrangian–Eulerian (ALE) method for dealing with free surface tracking, and considering turbulence effects in free surface flows. Several turbulence closure models are considered and compared, including two-equation models, namely k–ε and k–ω models, largely used in this kind of studies for their simplicity, and also a second-order Reynolds stress transport model R _ij –ε. In particular, we show that imposing additional boundary conditions at the free surface was crucial to model the interaction effects. Numerical results are compared with experimental data from [2] for the following four types of flow conditions: (1) only current, (2) only waves, (3) waves following current and (4) waves opposing current. A detailed study of the changes in the vertical profiles of mean horizontal velocities and shear stresses when waves and current interact is presented, with a discussion about the effects of the turbulence closure model used in the simulations.