2D numerical contributions for the study of non-cohesive sediment transport beneath tidal bores

Abstract

2D numerical simulations of tidal bores were obtained using the OpenFOAM CFD software to solve the Navier–Stokes equations by means of the Finite Volume Method by applying a LES turbulence model. The trajectories of non-cohesive sediment particles beneath tidal bores were estimated using a tracker method. Using the fourth order Runge–Kutta scheme, the tracker method solves the Maxey and Riley equations, which requires the knowledge of the velocity field at time t. From 2D numerical simulations of tidal bores, we proposed a classification of tidal bores with respect to the Froude number Fr (or r the ratio of water depths). For a Froude number 1<Fr<1.43 (1<r<1.57), the tidal bore is undular. For a Froude number 1.43<Fr<1.57 (1.57<r<1.75), the tidal bore is partially breaking, which is similar to the transitional tidal bore defined by Furgerot (2014). And for a Froude number Fr>1.57 (r>1.75), the tidal bore is totally breaking. The numerical results of trajectories of non-cohesive sediment particles are similar to the type of trajectories given by the analytical model proposed by Chen et al. (2012) with some modifications to take into account the effects of gravity, elevation, and attenuation. The parameters of modified Chen's model, β1, β2 and β3, are linearly proportional to the Froude number Fr. This is because the level of turbulence for undular tidal bores is low. The flow induced by an undular tidal bore is not complex. This physical phenomenon is quasi linear. The parameter β1, related to the front celerity of the undular tidal bore, decreases when the Froude number Fr increases. The parameter β2, related to the elevation, increases when the Froude number Fr increases. And the parameter β3, related to the attenuation of the secondary waves, increases when the Froude number Fr increases.