Numerical Research On The Transport And Dispersion Of Pollutants In Tidal Waters

Wastewater or heated water is frequently discharged instantaneously or intermittently into ambient flow. Near an ouffall, the discharged sewage mixes with the water of river or ocean. The velocity, pollutant concentration field and turbulent characteristics vary dramatically. This region is called the near-field. The water region beyond the near-field is called the far-field. The difference of hydrodynamic characteristics between the two regions is large. In the near- field, jet flow dominates while sewage is transported passively with ambient flow in the far-field. Usually, different mathematical models should be used. For this reason, different models are adopted and developed to simulate the transport and dispersion of conservative pollutants in this paper. There are two parts in the paper. Part 1: numerical simulation of the near-field. A depth-averaged mathematical model is developed to simulate anisotropic turbulent recirculating flows in an open channel, into which the heated-water is side-discharged. The model is an algebraic stress梖lux model (ASM) , which gives new expressions of stress components, and employs the depth-averaged continuity, momentum and temperature equations, which are solved by finite-volume procedure. This is the first time that depth-averaged ASM model is applied into the simulation of tidal flow. The work consists mainly of five aspects: 1. Introduction. Summarize the present research progress and application of two-equation turbulent flow model and ASM. The contents and numerical methods in the thesis are set forth. 2. Content of the model. It consists of two chapters. In the second chapter, the origin and content of depth-averaged ASM are introduced. Its numerical method is described in the third chapter. 3. Numerical simulation of steady flows. The flow and the concentration field are simulated when hot water is side-discharged into an open channel. Predicted size of the recirculation zone and isotherms are compared with those of experiment and the results of k ?e model. The results show good agreement with experiment data and logical trend of expansion of recirculation zone. The stress and flux components show the an isotropy of the model. 4. Numerical simulation of unsteady flow. The tide is asymmetric. The results show the changes of velocity field and pollutant concentration with time and space during one tidal period. The better agreement with experiment than depth-averaged k model verifies the superiority of the depth- averaged ASM. 5. Discussion on the model. Part 2: numerical simulation of the far-field. A semi-implicit three-dimensional ocean circulation model is employed to simulate the tidal flow of Hangzhou bay and Changjiang river estuary. a?coordinate is adopted in vertical direction, It permits the use of fine vertical resolution in the surface and bottom boundary layers. Both analytical solutions and real salinity field calibrate the numerical scheme. The work consists mainly of three aspects: 1. Introduction. In the seventh chapter, The development and present progress and application of three dimensional tidal model are summarized, the differences among these models are concluded. 2. Content and characteristics of the model. It is composed of two chapters. The development, content and the characteristics of the model are introduced in the eighth chapter while the numerical m...