Large Eddy Simulation Of Turbulent Structure In Compound Meandering Channels

The compound meandering channel is a common channel pattern in nature.Influenced by compound cross section and curve,it has complex and varied flow structure and great impacts on sediment deposit,river bank erosion,nutrients transport and river migration.At present,the understanding of compound meandering channel is not sufficient.In this paper,large eddy numerical simulation method(LES)and cylindrical coordinate system is adopted and the corresponding governing equations of flow are deduced.After verifying the feasibility of the model using the experiment results,the variation patterns of the main flow,circulation,pulsation and Reynolds stress in the compound curved channel are studied under different working conditions.The simulation results show:(1)The secondary flow intensity caused by compound cross section is related to the depth of the shoal,and it declines with the decrease of the ratio of the depth of the shoal to the main channel.However,if the ratio is too large or the depth of the shoal is close to the main channel,the velocity distribution of the whole complex section will be close to the rectangular open channel,meanwhile the secondary flow intensity will get smaller.When the ratio of the depth of the shoal to the main channel is about 1/2,the secondary flow strength is the largest,which is 5% of the average flow velocity of the main channel.(2)The intensity of lateral circulation in meandering channel is affected by the width and depth of river channel.And along with the increase of channel width and water depth,the transverse circulation intensifies.In the working conditions simulated in this research,the maximum lateral flow intensity caused by the curve is 3.5% of the average flow velocity of the main channel.(3)The flow structure in the compound meandering channel is not a simple superposition of the flow structures in the compound channel and meandering channel.The simulation results show that the maximum circulating current intensity is 3.5% of the mainstream intensity,which indicates the circulation strength generated by the centrifugal force dominates.And altering the location of the shoal of the main channel has great influence on the flow structure in compound meandering channel.When the shoal is in the concave bank,the water movement in the shoal is more complex and the intensity of the water mixing in the main channel is significantly larger than in the convex bank.This study has revealed the hydrodynamic regularity in the compound meandering channel,which is of great significance to further understanding of the flow structure,sediment transport and pollutant dispersion in the compound curved channel.