Coupled Simulation of Flow, Sediment Transport and Morphology Evolution Over Ripples Based on the Immersed Boundary Method

Georgios Leftheriotis, Athanassios Dimas

Thursday 2 july 2015

15:05 - 15:20h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 12A. Sediment - Transport

In the present study, numerical simulations of oscillatory flow over ripples, coupled with bed and suspended sediment transport, as well as the resulting morphology evolution, are performed. The simulations are based on the numerical solution of the Navier-Stokes equations for the flow and the advection-diffusion equation for the suspended load, while empirical formulas are used for the bed load. The bed morphological evolution is obtained by the numerical solution of the Exner equation. A fractional time-step scheme is used for the temporal discretization, while finite differences are used for the spatial discretization on a Cartesian grid. The Immersed Boundary method is implemented for the imposition of fluid and sediment boundary conditions on the moving bed surface. Three cases of mobility number were examined, _ = 4, 10, 40, at Reynolds number equal to 5×10^3. The vortices generated on the lee side of the ripples are highly correlated with the behavior of the suspended sediment. Both suspended sediment concentration and bed load transport magnitude increase with increasing mobility parameter values. The evolution of suspended sediment is highly correlated to the vortical structures.