Lattice Blotzmann Simulation For Effects Of Salinity On Flocculation Of Cohesive Sediment

The flocculation processes play an important role in cohesive sediment transport and some physical phenomena in estuaries and on coasts. Moreover, salinity is the one of the main factors which influence the cohesive sediment flocculation. However, there is few effective ways for direct numerical simulation of salt flocculation mechanism. Therefore, a three-dimensional numerical model of salt flocculation dynamics of cohesive sediment via the Lattice Boltzmann method was presented. Some physical phenomena in the field were explained from the mesoscale view. The main results are summarized as follows:1. A fully resolved numerical model of salt flocculation dynamics of cohesive sediment via the Lattice Boltzmann method was developed. The simulated results agreed with those analytical solutions. It was shown that the present model could be applied to the simulation of the effects of salinity on the flocculation behavior.2. The processes of two settling particles under different salinity situation were obtained. It is shown that the salinity mainly influences the minimum distance between the two particles during settling. The higher is the salinity, the smaller the distance between two particles will be. It is also observed that in the high salinity situation there is a sudden-change of relative velocity of the particles, while this cannot occur in the low salinity situation.3. The salt flocculation processes due to differential settling of cohesive sediment in different salinity situation were simulated via Lattice Boltzmann method. The higher the salinity is, the smaller the electrical double-layer interaction force is, which makes it easy to aggregate. In high salinity situation, the single particles or the flocs may collide with the other particles or flocs and aggregate during settling. The flocculation processes of multi-particles form the complex flow fields around the particles, which change the particle trajectories and settling velocities, and then make the flocs rotate in water.