Numerical Simulation Of Two-dimensional Transient Temperature Field Of Riverbank Filtration System Based On Temperature Tracing

Riverbank filtration is a typical surface water-groundwater interaction process.The bidirectional exchange process of material and energy in the riverbank filtration system is an important way to maintain the material circulation,energy exchange,information flow and other environmental behaviors in the ecological corridor between the river and the adjacent groundwater system.Mastering the heat transfer in the riverbank filtration system is an important means to quantitatively analyze the seeapge exchange flux and identify the potential chemical and microbial reaction intensity in the filtration process,which is of great significance to the water quality assurance of riverside water sources.Based on the laboratory experiment and numerical simulation research on the temperature field distribution law of heterogeneous aquifer in the riverbank filtration system under different scenarios are carried out.It is helpful to reveal the two-dimensional transient variation law of temperature field of heterogeneous aquifers in riverbank filtration system,which provides scientific and technological support for the water quality security of riverside water source areas.The main research work and results are as follows:(1)By carrying out sand tank experiments at different temperatures of the infiltration river water temperature,the influence of river water infiltration temperature on the temperature field of the heterogeneous aquifer in the riverbank filtration system was studied on a two-dimensional scale.The results show that with the increase of infiltration water temperature,the shallow area of temperature field of heterogeneous aquifer in the bank filtration system is more affected by infiltration water temperature than the deep area.In the horizontal direction,the temperature field gradually diffuses from the infiltration point to the distance affected by the infiltration water temperature.(2)Based on the physical model of laboratory sand tank experiment,the water and heat migration model of heterogeneous aquifer in riverbank filtration system is constructed.The root mean square error(RMSE),coefficient of determination(R~2)and relative error(Re)are selected to evaluate the simulation accuracy.According to the verification results of laboratory experiments,the RMSE value of FEFLOW finite element software for model simulation ranges from 0.12°C to 0.77°C,the R~2 value ranges from 0.87 to 0.99,and the Re value ranges from 0 to 5.22%.Experimental temperature and simulation temperature is good in effect of fitting,indicating that the hydrothermal migration model of the heterogeneous aquifer in the riverbank filtration system established based on the laboratory sand tank experiment has high reliability.It is feasible to use this model to analyze the distribution law and dynamic change characteristics of the two-dimensional transient temperature field of the heterogeneous aquifer in the riverbank filtration system.(3)Based on the established water and heat migration model of heterogeneous aquifer in the riverbank filtration system,the temperature field of heterogeneous aquifer in riverbank filtration system under different scenarios was simulated and analyzed.The results show that the permeability coefficient of aquifer medium is the main factor affecting the temperature field distribution of the riverbank filtration system.The influence of the infiltration river water temperature and head on the two-dimensional temperature field distribution of heterogeneous aquifer in riverbank filtration system shows significant dynamic changes.In the range of water withdrawal set by the model,the influence of water withdrawal on the temperature field of heterogeneous aquifer in the riverbank filtration system can be ignored.