Application Of Temperature Tracer On The Law Of Downstream Hyporheic Exchange Of The Dam

After the dam is built,the water level in front of the dam is raised,and the temperature difference between the discharge water temperature and the original river channel is significantly different,resulting in a change in the temperature field within the original river bed subsurface zone,which has a greater impact on the ecological health,material and energy exchange in the region.It is of great significance to study the effects of water temperature T,flow velocity v,water level H,bed permeability k,and sand slope height h on the temperature distribution of the subsurface flow channel of the dam.Based on Reynolds's average equation(N-S equation),k??turbulence model,Darcy equation and heat conduction equation,this paper uses the CFD-Fluent and COMSOL Multiphysics software to construct the surface water-groundwater coupling model of the riverbed downstream the dam,and discusses the Morris global sensitivity analysis method,Single-factor effects and multi-factors influence the temperature field variation of the river bed under the dam.The research content and conclusions of this paper are as follows:(1)Based on the two-dimensional surface water-groundwater coupling model constructed,it can be known from the analysis of single influencing factors that the pressure peak appears at about 1/2 of the water surface,the pressure trough value appears at the peak of the sand slope,and the negative pressure area exists at the back water surface;The depth of the surface is about 0.1?0.2m,which is obviously affected by the temperature of the river.Temperatures at the monitoring points(2.75,-0.1)and(2.75,-0.2)have reached steady state before the completion of the simulation 24h;and they will meet in the lower part of dune.A semi-circular low-temperature zone appears,and as the depth of the river bed subsurface flow in the vertical direction increases,the effect of water temperature gradually weakens.the effect of water temperature gradually weakens.(2)According to the Morris global sensitivity analysis,the influence of flow velocity v,water temperature T,water depth H,bed bottom permeability coefficient k,and dune height h on the temperature field of the river bed subsidence zone weakens in turn.At the same time,it can be concluded that water temperature T and depth H are positively correlated with temperature field changes,and other factors are negatively correlated.(3)Comparing the calculation results of the three-dimensional model with the two-dimensional model,it shows that the increase of the water temperature T,the flow velocity v,and the permeability coefficient k,the temperature field of the subsurface flow zone is more obvious than the calculation result of the 2D model.While keeping other influencing factors unchanged,when the flow rate is increased by 20%,the pressure difference between the three-dimensional model and the two-dimensional model increases by 8.39Pa in the direction of the downstream flow compared to the calculated results of the two-dimensional model,and there is a low temperature area in the lower part of Shapo.The trend of downward movement.When the water depth was increased by 20%,the pressure difference between the three-dimensional model and the two-dimensional model increased by 1.66Pa in the direction of the downstream flow compared with the calculated results of the two-dimensional model,and there was no significant difference between the three-dimensional model and the two-dimensional model.