Flow Structure And Resistance Characteristics Of Open Channel With Large Scale Rough Bed

It is common for open-channel flow with Large-scale roughness in natural mountain rivers and river model tests.Their velocity distribution,turbulent structure and resistance coefficient are different from those over small-scale rough beds.It is very important to study large-scale roughness flow for the development of mountain rivers and in the study of roughness hydraulic models.However,the related research is still weak at present and needs further study.So,in this paper,the influence of the particle shape and arrangement spacing on the flow structure and the influence of density of arrangement when the bed is a plum blossom on the flow structure and resistance is studied through the flume test.All the flow is in large-scale roughness condition.The main research results are as follows:(1)The elliptical threshold method is used to deburr the flow rate signal measured by Doppler effect,and then it can eliminate high frequency noise by using db3 wavelet threshold denoising.(2)The three shapes of the single particle are surrounded by a downward U-shaped flow.The longitudinal velocity plane is elliptic around the cube and the tetrahedron,and a bell shaped upward around the sphere.The vertical flow velocity is linearly distributed when the flow velocity is small.When the velocity is larger,the vertical distribution of longitudinal average velocities downstream of the cube particles is S-shaped and then linear distribution,and is linearly distributed downstream of the sphere and tetrahedral particles.In the downstream of all particles,more to the downstream,the Longitudinal velocity is more uniform When the velocity is larger.At low speed,the turbulence intensity around the cube particles is more evenly distributed,and the turbulence intensity around the sphere and tetrahedral particles gradually increases from the water surface to the bed.When the flow velocity is larger,the vertical distribution of the turbulence intensity is more uniform.(3)With the increase of the distance between the two rows of horizontal particles,the shape of the wave around the surface of the surrounding water fluctuates from one U shape to two U shapes.The vertical distribution of the longitudinal flow velocities in the middle vertical plane changes from a linear distribution to an even distribution,The intensity becomes smaller;the effect of transverse spacing on the longitudinal flow velocity distribution is greater up the top of the particles than down the top of the particles.(4)Longitudinal double particles will form several undulating U-shaped fluctuations along the downstream of the upper particles.Longitudinal spacing has little effect on vertical distribution of longitudinal velocity and turbulence intensity of the upstream and downstream of the double particles.Increasing the longitudinal spacing will weaken the particles Turbulence intensity between particles.(5)The increase of density of plum blossom surface roughness will reduce the undulation amplitude of water surface;the longitudinal gradient of longitudinal flow velocity is positively correlated with Fr and negatively correlates with the density of particles;the vertical distribution of longitudinal velocity is linear;the turbulence intensity and turbulence The dynamic shear stress obeys the linear distribution above the top of the particles,and the second-order moments of the pulsating velocity in three directions are close to each other.(6)The formula of Stefano Pagliara is revised and a new calculation formula of the resistance coefficient of water flow over the large-scale rough bed is obtained based on the experimental data of water flow resistance in this paper.