Study on the flow structure in curved open channels with suspended vegetation using multi relaxation time lattice Boltzmann method

Abstract

Suspended vegetation in rivers, lakes, reservoirs and canals can change flow structure, which will in turn affect the sediment transport and cause the variation of water ecological environment. In order to study the characteristics of bend flow through suspended vegetation, three-dimensional numerical simulations are carried out by using the multi-relaxation-time lattice Boltzmann method (MRT-LBM). The drag force induced by vegetation is added in the velocity correction in the equilibrium distribution and a hybrid format combined bounce and specular reflection scheme is applied in the solid-fluid boundaries. After the validation of this model, six cases are designed to conduct the numerical simulations according to the root depth and the arrangement of vegetation. The simulated results show that the suspended vegetation can redistribute the flow structure in curved open channels. After the arrangement of suspended vegetation, the main flow moves to the side without vegetation, and the distribution of velocity tends to be balanced when vegetation is arranged on the entire cross section, the range of circulating current is reduced from the whole cross section to the local position without vegetation, however, the circulating current can still exist in the curve where the suspended vegetation enters less than half of the water depth. In addition, it can also be concluded that the suspended vegetation can affect the lateral gradient of flow velocity, and the bed shear stress in the curved channel.