Analysis On Water Transport And Concentration Field In Lakes With Multi-inlet And Multi-outlet

Constructing water diversion works gradually became an effective method in rehabilitating the urban lake. After diverting water, the lake had several inlets and outlets, swallow-spit current became the uppermost factor. The study on the flow field and the concentration field of the lake with multi-inlet and multi-out can forcast and evaluate the improvement effect of the lake water due to the water diversion works.In this paper, the West Lake was taken for example, and a 2D hydraulic and water quality model was established for the West Lake. The model was applied with the finite volume method, and calculated by PHOENICS. The flow field and the concentration field of the whole West Lake were simulated, and the simulated results were in visualization. According to the actual water distribution scheme, the model set 9 inlets and 10 outlets, and the mesh of the whole calculation domain was 400*400. 6 operating cases of the flow field were calculated, and the flow field figures of the six cases were given. The concentration field which marked with total phosphorus was established. On the basis of analyzing and estimating the source of total phosphorus that went into the West Lake, the main sources were confirmed. They are the carry-over of the streams, the sediment releasing and the carry-over of the water from Qiantang River. Estimated the total phosphorus data of them as the boundary condition in calculating, Then according to the actual water diversion and water distribution of the West Lake of the four seasons in 2004, the source of total phosphorus and the data of the 11 concentration field measuring point, inversion analysis was carried out, then the comprehensive sedimentation constant k was obtained. Then on the basis of the model and the parameter, given the data of the actual water diversion and water distribution of the West Lake of the four seasons in 2005, the corresponding steady concentration field situation of the West Lake was forecasted. Finally, verification was done, using the data of the 11 concentration field measuring point of 2005. The calculation data approached the measuring data. It indicated that the concentration field analysis model, the calculation parameter and the boundary condition were all reasonable and reliable.In this paper, the data including the water diversion and water distribution of the West Lake and the total phosphorus in 2004 was chosen as the operating mode, and the simulation of the unsteady concentration field situation of the West Lake was done. And the dynamic process of the water transport and the evolution of the concentration field was shown.The numerical analysis results indicated that the present collocatation and distribution of the inlet and the outlet was good. Especially after the 4 inlet around the west-expanded waters and the Changqiaowan inlet were added, the flow fields of the west-expanded waters and Changqiaowan waters are better now. The total phosphorus flat distribution is relatively uniform. The whole flow field of the West Lake only has several places where the current velocity is very low, and the areas of these places are small.The hydraulic and water quality model established in this paper and the analysis method adopted can provide references to the numerical simulation analysis on the flow field and the concentration field of the similar multi-inlet and multi-outlet lakes.