Lattice Boltzmann numerical simulations of wave-current interaction within the boundary layer

In this work, numerical simulations of the oscillatory boundary layer induced by an oscillatory-ripple-covered bed in a fluid otherwise at rest and in the presence of superimposed weak currents are presented. The simulations are performed using a rather new promising numerical technique named the Lattice Boltzmann Method and a brief description of the method is given. The dynamics of coherent structures in the boundary layer are presented. The results show a cycling repetition of jet of vortices from the boundary. Their interaction lead to a momentum transportation at a distance from the boundary that decreases for increasing value of the tested superimposed currents. For the lowest values of the superimposed currents, time-averaged velocity fields as well as time-space-averaged velocity profiles show the formation of a streak of fluid, close to the ripple crest level where the velocity is against the current.