Large-eddy simulations of turbidity plumes in crossflow

Two-phase Large-Eddy Simulations (LES) of turbidity plumes in a crossflow are presented, representative for mixtures of water and fine sediment particles released through an overflow pipe of a dredging vessel. The model was tested based on experimental data of vertical plumes in a still environment as well as of plumes in crossflow. Simulations include the effect of the wake of a schematised hull shape on the dispersion and turbulent structure of the plume, as a schematisation of plumes released from dredging vessels. Criteria for a minimum fraction of resolved turbulent kinetic energy were used to evaluate the so-called completeness of the LES simulations. It is shown that while the grid resolution is a factor three to six lower compared to earlier Direct Numerical Simulation (DNS) simulations, comparable results on turbulent structures and turbulent kinetic energy can be obtained. Results of mean trajectory and plume dispersion show good agreement with experimental data. The different types of turbulent structures found in our experiments as well as in literature are reproduced by the model. It is shown that a release point shortly upstream of the schematised hull's stern causes the upper fringes of the plume to be torn off in cases with a relatively strong crossflow, which enhances mixing and hampers the containment of the material transported by a plume.