Three-dimensional Numerical Simulation Of Cooling Water In Longkou Northern Waters

With the development of national economy and the increasing electric power demand in our country, coastal power plants have been built rapidly. These power plants usually use the seawater to cool the units, with the obvious advantage of enough water source and remarkable cooling effect. But discharging the cooling water to the outfall can always cause the water temperature in power plants area raising some degree, disrupt the original water temperature distribution and bring violent shock to ecological environment. Meanwhile, this method may affect the cooling water temperature of the plant itself and threaten safety and stability of units. Therefore, numerical prediction and research of the cooling water have the great significance of environmental protection and engineering design.Taking example of Longkou plants drainage area, a 3-D cooling water numerical model is built up based on the unstructured grid finite volume coastal and ocean model(FVCOM). The model can accurately fit numerous islands in the northern of Longkou seawater area and tortuous irregular shoreline boundary in the horizontal direction by using unstructured triangle meshes; in the vertical direction, the model is able to describe complex terrain by using σ coordinate. On this basis, current and tide data of research area was used to verify the hydrodynamic model, and multiple cross section observational data of temperature was also used to calibrate the model parameters. Furthermore, the numerical simulation results are in line with the measurement data, which shows the reliability of the model. High resolution(the space step is less than 30m) temperature field simulation results are obtained after researching on horizontal water temperature distribution and typical sectional characteristics in three design conditions of summer, winter and autumn(spring). The results showed the great consistency of numerical sea area results and the observation data. The results of FVCOM model are basically identical with the 2-D simulation results based on the Mike21 model widely used, which proved reliability of the model further. Stratification phenomenon caused by inadequate vertical mixing is showed in the FVCOM model, which reflects the actual situation of real cooling water drainage. So the model in this paper built can not only obtain the correct 2-D numerical results but also get the hydrological section structure which can not be simulated in 2-D model.The model results show that the differences of temperature field horizontal distribution are significantly affected by the tidal current, water depth and topography. High temperature water mass discharged at the outfall flows more rapidly carried by the tidal current because of the strong hydrodynamic condition in the spring tides season, then the transport diffusion scope of high temperature water along the flow direction becomes lager. While the situation in the neap tide season is contrary. The special topography close the drain also influences the movement of the cooling water significantly, which is found that the high temperature regional coast line presents the zonal distribution because of the blocking function of the underwater sand ridges to the water mass heat along offshore direction. The seasonal differences of the cooling water influence scope are remarkable, which are reflected as more temperature-rising influence scope in winter than other three seasons. The temperature rise of the sea water presents obvious vertical distribution differences because of the direct effect of water temperature on density in the typical section. Meanwhile, the model reflects the “temperature jump” phenomenon appeared in the process of measuring at individual observation stations, and it can be explained in the mechanism that the phenomenon is caused by the high temperature offshore water jetting at some special time.