Study On Pollutant Concentration Field In The Water Body With Flume Experiment And Numerical Simulation

The research in diffusion and mixing characteristics of pollutant discharge into environment water has important guiding significance and practical value in engineering practice such as the design of sewage pipe and diffuser, the choice of discharge water and emissions way, the water quality prediction, the water quality planning and the water conservation etc.Firstly this paper summarizes and analyzes measuring methods of pollutants concentration at home and abroad, and determines to use quantitative digital image processing technique as the concentration measurement of this study. Then do research in the distribution of pollutant concentration field in the water body by using physical model experiment and numerical simulation method.The physical experiment mainly establishes the measuring method of pollutants concentration in water in the lab,this method is more scientific and accurate which provides a practical method for measurement of pollutants concentration in water in the lab. And the mensuration composed of calibration of pollutant concentration and flume experiment.In calibration experiment, calibrate the pollutant concentration in still water and dynamic water respectively. Then get the two relation curves of pollutant concentration and the image gray level. By comparing the relation curves, we can find that pollutants calibration concentration in dynamic water is closer to the flume experiment in the aspects of equipment layout and other external conditions. So we choose the relation curve of calibration in dynamic water as the final calculated curve to calculate the corresponding relation between gray and concentration.In flume experiment, experiment with different flume influent flow and pollutant discharge flow. Experimental results show that:(1) In the case of certain pollutants discharge flow, with the increase of flume influent flow, the direction of velocity close to the direction of X axis gradually, and the influence of the discharge of pollutants to the environment flow field is smaller and smaller;(2) In the case of certain flume influent flow, with the increase of pollutants discharge flow, the direction of velocity deviate from the direction of X axis gradually, and the change of flow field near pollutants discharge outlet is more and more obvious which means the influence of the discharge of pollutants to the environment flow field is bigger and bigger.(3) In the case of certain pollutants discharge flow, with the increase of environmental flow, the boundarys of the concentration contour map contract to the middle gradually, the diffusion width of concentration contour become smaller gradually, and concentration path line moves towards the left side of the flume near the outlet;(4) In the case of certain flume influent flow, with the increase of pollutants discharge flow, the boundarys of the concentration contour map expand to the sides gradually, the diffusion width of concentration contour become larger gradually, and concentration path line moves towards the right side of the flume near the outlet;In numerical simulation, using MIKE3 to simulated the distribution of velocity field and pollutant concentration field in water numerically. Verify the numerical simulation with the water level data, velocity data and concentration data compiled by the physical experiment. Fitting result is good. And on this basis, simulated the distribution of pollutant concentration field under different conditions(the conditions are same as the physical flume experiments’) respectively. And results show that:(1) In the case of certain pollutants discharge flow, with the increase of flume influent flow, the velocity field changes in the area which are that, velocity in whole area increasing, the velocity decreasing areas near the pollutant discharge outlet become smaller and smaller,the direction of velocity close to the direction of X axis gradually, and the changes of velocity field lead to changes of the concentration field which are that, asymmetric concentration area decreasing, the boundarys of the concentration contour map contract to the middle gradually, the diffusion width of concentration contour become smaller gradually, and concentration path line moves towards the left side of the flume near the outlet;(2) In the case of certain flume influent flow, with the increase of pollutants discharge flow, the velocity field changes in the area which are that, the velocity decreasing areas near the pollutant discharge outlet become larger and larger,the direction of velocity deviate from the direction of X axis gradually, and the changes of velocity field lead to the changes of the concentration field which are that, asymmetric concentration area increasing, the boundarys of the concentration contour map expand to the sides gradually, the diffusion width of concentration contour become larger gradually, and concentration path line moves towards the right side of the flume near the outlet.