Experimental Study On Turbulence And Suspended Sediment Characteristics Of Salt-wedge Interface In Muddy Water Environment

When the two fluids with different density meet,the fluid with relatively large density will dive under the action of gravity and form a heterogeneous flow under the influence of gravity.In the natural environment,there are a lot of heterogravity flow phenomena and processes.As a typical branch,the saltwater wedge plays an important role in the environment around the estuary.The hydrodynamic characteristics of the interface between saltwater and fresh water are of great significance to the transport of environmental materials in the water wedge gravity flow.The study of hydrodynamic suspension process at the interface of salt water wedge is helpful to understand the sediment transport characteristics in the estuary area,and thus plays an active role in the comprehensive analysis of the changes of water environment in the estuary.In this paper,the process of sediment suspension at the interface of salt water wedge density current in muddy water environment is studied by flume experiment.The high frequency Doppler acoustic velocity profiler(advp)is used to measure the turbulent velocity,and the back scattering sound intensity signal of advp is used to retrieve the sediment concentration.The temporal and spatial distribution of velocity and sediment concentration near the interface under experimental conditions is obtained,The turbulence index,stratification coefficient and turbulent length scale of stratified flow at the interface are calculated and analyzed.Combined with the development of interface unstable wave,the influence of hydrodynamic evolution of salt water wedge interface on sediment concentration of environmental flow is explored,and the correlation between them is explored,and then the mechanism of salt water density flow on sediment suspension and transport is discussed.The main research contents and achievements are as follows(1)The semi empirical inversion formula between advp sound intensity signal and sediment concentration is determined.The applicability of the formula is verified in experiments.(2)Under the uniform muddy water environment in the laboratory,there is a high concentration of sediment mass near the interface of salt water wedge,which is higher than the zero velocity layer of the interface.The average thickness of the high concentration zone increases gradually from the head of the saltwater wedge,and the sediment concentration above the high concentration zone has no obvious change.(3)The results show that the interface turbulence of salt water wedge increases obviously,and the higher the interface is,the more obvious the interface turbulence is.In the front of the salt water wedge,the interface layer is dominated by K-H wave and has the characteristics of strong turbulence and strong mixing;As the unstable process gradually transits to the holmboe wave stage in the back part of the saltwater wedge,the turbulence decreases and the stratification increases,but the vortex length scale increases.(4)In different stages of unstable waves,the correlation between sediment concentration and hydrodynamic parameters is different,and turbulence intensity and velocity gradient occupy a higher position.Meanwhile,the influence of turbulence intensity and velocity gradient on sediment concentration lags behind.