Numerical simulation of sediment transport by thermohaline bottom currents

Contour (along slope) and turbidity (downslope) currents actively interacts on the seafloor of the continental margins and control the distribution of seafloor habitats, slope instability, microplastics accumulation and hydrocarbon reservoirs. Numerical simulations that reproduce the sediment transport at the crossroad of these two current types may improve the understanding of this distribution. Nevertheless, the interaction between turbidity and contour currents is problematic to afford with numerical or experimental instruments. The aim of this PhD study is to adapt and develop methods for the numerical simulations to reproduce the effect of this interaction on the sediment transport in order to understand how the finer (suspended) component of the sediment transported by the turbidity flows can be a source of sediment for transport within the contour current. The first step of the project will be the construction of a pertinent domain. For this purpose, the intention is to use a setting where a straight inclined channel (for the release of the turbidity flow) leads to an expansion table covered by sediment and swept by a transversal contour crossflow. With respect to this case, to better represent our phenomenon, the turbidity current channel will be considered with a talweg lower than the expansion table. After this first step, we will analyze the two types of currents independently, turbidity and contouritic, using the reference literature for comparison. This will be useful to better understand the critical characteristics of the two currents, and the possible problems posed by their interaction. In the end, as a third step, the turbidity current will be analyzed in the case of contour crossflow, with a particular attention to the possible mechanisms of sediment transport. Considering the complexity of the mixing processes of the two currents type and of their interaction, we will take advantage of Large Eddy Simulation (LES) or of Wall-modelled LES (i.e. skipping the solution of the viscous boundary layer). The cases will be analyzed at a time scale related to the turbidity current. The sediment transport, for computational reason, will be probably treated with a Eulerian approach, therefore through the solution of the transport equation for a scalar, with a two - way coupling of the momentum equation through the buoyancy term.