Study On Numerical Simulation Of Hyporheic Exchange Driven By Triangle Riverbed

The interaction of river surface water-groundwater is an important process of the Earth's hydrological cycle.Hyporheic exchange is an important process in the surface water-groundwater interaction in the hydrological cycle.It controls the transfer of matter and energy between surface water and groundwater and affects the biochemical reactions in the hyporheic zone,thus affecting the ecological health of the basin.This paper uses COMSOL and CFD-Fluent combined numerical simulation method to construct the surface water-groundwater coupling model under the influence of triangular riverbed morphology based on Reynolds average equation(RANS),k-? turbulence model and Darcy equation.Therefore,this paper mainly analyzes the flow characteristics of surface water turbulence,the flow analysis of water-sediment interface and the flow analysis of hyporheic exchange area,and explores the hyporheic exchange law of surface water and groundwater under the influence of geometric shape of triangle riverbed.The main research contents are as follows:Based on the existing generalized water tank test to test the surface water velocity distribution model,the simulated sixth sand dune velocity and velocity curves are validated.Turbulent flow of surface water under the influence of triangular riverbed can be well characterized by the constructed surface water-groundwater model.The triangular riverbed has a great influence on the pressure and velocity distribution at the water-sediment interface.The angle of the water-slope slope of the triangular riverbed is inversely proportional to the pressure at water-sediment interface,and is proportional to the flow velocity at the peak.The inlet flow velocity of surface water is proportional to the extremum of pressure at water-sediment interface,and is proportional to the flow velocity at water-sediment interface.The maximum values of turbulence intensity and wall shear stress appear stably at the peak of the triangular riverbed,indicating that the peak shape of the triangular riverbed is more susceptible to changes in surface water turbulence.Aiming at different triangle riverbed patterns,a method for determining and quantifying the up-flow and down-flow of water-sediment interface is proposed.The distribution of up-flow and down-flow at water-sediment interface basically depends on the geometry of the riverbed,and its distribution basically does not change with changes in surface water velocity.The crest is a stable demarcation point between the up-flow and the down-flow,and hyporheic exchange flux is negatively correlated with the angle of the sloping slope.When the morphological changes of the riverbed change,the distribution of the positive and negative exchange zones changes,and it basically does not change with changes in surface water velocity.There is a stagnation zone in the hyporheic zone where the lateral flow velocity component and the vertical flow velocity component respectively approach 0,and its depth is similar to the depth of the hyporheic zone.The lateral stagnation zone is located near the boundary of the reverse exchange zone of the hyporheic zone,and the vertical stagnation zone is located on both sides of the maximum value of water-sediment interface pressure.