A Three-dimensional Numerical Simulation Of Mixed Current In West Lake

West lake, a famous tourist spot, has very important touring value and environmental significance. Before this, the study on the west lake was focused on the source of eutrophication and its countermeasures, even the flow and water quality simulation were centered on 2-D model for the past few years. However, the west lake, a sallow lake, the flow field is influenced by wind-current obviously and the flow structure has very noticeable 3-D character under the action of wind field. Therefore the study on the flow field and pollutant concentration field is very important to improve the water quality of the west lake.A 3-D mathematical model, which was based on ADI algorithm, was constructed by using software-Delft 3D to simulate the west lake's hydrodynamic environment under the action of wind field, and especially study the character of mixed current field and the diffusion rule of the pollutant. The calculations were well tallied with the measured data, which proved the model was true and credible.The results of numerical simulation show that the flow field under wind was settled after 4 hours and was sliced vertically. The surface direction was agree with wind direction, as the bottom compensation current direction was opposite with it. The current velocity in each part of the west lake was accelerated obviously, and the range was decided by wind direction, which reached the maximum under the southwester.The results of numerical simulation show that the concentration distribution of pollutant was vertically averaged under the action of vertical diffusion, no matter it's windy or not. The west lake can be totally exchanged by abstraction under each condition. Limited by its geographical position, the positions of inlet and outlet, and the diffusion rule of the pollutant in Wai lake (a part of the west lake), the water quality in Beili lake (a part of the west lake) may be improved by exchange of water only when the pollutant concentration was lower (about 30 days later) in the northwest corner in Wai lake, Gu hill and Bai Causeway.