Three-dimensional Numerical Simulation Of Flow, Sediment Transport And Scour Around A Pier In The Yangtze River Estuary

In this paper, we use the ECOMSED model to simulate the flow and sediment transport in the Yangtze River estuary and the adjacent area. At meantime, we fully analyze and discuss the survey data. The following conclusions are obtained throughout the work: it is non-formal shallow semidiurnal tide in the estuary. The ebb tide is much stronger than the flood tide, and the velocities decrease along the depth. The distribution of suspended sediment concentration is associated with the velocity. The concentration becomes higher when the velocity increases. The sediment can be resuspended four times during one tidal period at most. Two times happen at the maximum velocity time of ebb tide and flood tide separately, and the other two happen during the current turning periods. There will be a saline-water intrusion front during the current turning period, and this is the cause of the sediment re-suspension. The vertical distribution of suspended sediment concentration can be divided into four patterns: beeline, diagonal line, parabola and L-shaped. The flow pattern and bed change are associated with the water depth. The velocity is bigger and the bed change higher where the water is deep. The sediment deposits at the riverine current area and suspends at the tidal current. The sediment generally deposits at shallow water.Comparing the simulate results with the survey data, we conclude that the model can simulate the flow pattern, sediment transportation, salinity distribution and bed change properly. It is of great significance to us to understand the Yangtze River estuary.A three dimension Eulerian two-phase numerical model for the simulation of flow pattern and local scour around a pier is presented, too. Both flow-particle and particle-particle interactions are considered in the model. The results show that the velocity field and local scour around the pier is reasonable. In front of the pier, the velocity decreases and forms a vortex which induces the scour hole. At both sides of the pier, the velocities accelerate, and laminated load is accumulated nearby. Behind the pier, there is a separation zone with two symmetrical eddies when the inflow velocity is about 1.1 m/s. In this separation zone, velocity magnitude is the least, and local scour around the pier is the weakest, even deposit happens for a long run.The scour hole around the pier is more evident at higher velocity because of the vortex formed in front of the pier. The bed is easier to scour when the grain size is small, because the critical stress of bed is small. The sediment concentration is associated with velocity, and the sediment could be suspended to a higher layer when the grain size is small and the velocity is high.