In order to study the influence of vegetation patch and bed roughness on flow characteristics in river,this paper used wooden cylinders to simulate emergent circular patch composed by different plant density,with movable bed and fixed bed conditions.By using flow velocity and turbulence kinetic energy,this paper analyzed the formation and development of the upstream adjustment length and the wake flow.Firstly,the results showed that when the diameter of the patch was constant,the upstream adjustment length of patch is independent of vegetation patch density,and in this experiment,the effect of bed roughness could be ignored.Secondly,this paper used the volume fractionφas a comprehensive characterization of density and diameter of patch.Comparing the contribution of bed roughness and the volume fraction to the complete wake length,it was found that the complete wake lengthLwas related to the volume fractionφ,amely,whenφvalue was larger the length of the complete wake was smaller.Thirdly,the velocity distribution was mainly controlled by the bed roughness and the volume fraction value backward of the vegetation patchand the steady wake lengthL1value was related to theφvalue,withL1/Dreaching the maximal value in the vicinity ofφ=6%.Finally,two turbulence kinetic energy peaks generally appear on the wake region,with its location being mainly affected by the density of patch and the roughness of bed.Due to the different densities of vegetation patch,the development of energy exchange and transverse shear layer was not the same in the wake structure,which was the main factor that affects the position of velocity returning to normal velocity and the formation of stable wake.This paper can provide a reference for the further analysis of the interaction between water flow and vegetation under different bed roughness.
