【作者】 王进行；

【导师】 黄廷林；

【作者基本信息】 西安建筑科技大学 ， 市政工程， 2010， 硕士

【摘要】 扬水曝气是为解决大水深水库水体富营养化、底泥内源污染物释放等问题而开发的新型水质原位修复改善技术。扬水曝气器通过间歇性的气弹向水体充氧提高底部溶解氧改变下层水体的厌氧状态,控制底泥中的氮、磷、铁、锰、有机物向水体释放。通过曝气造成水体上下层之间混合,破坏大水深水体的温度分层现象,并可使表层藻类向下迁移至无光区域,从而抑制藻类的生长,最终致其死亡。计算流体力学(CFD)技术利用离散化的数值方法和计算机,通过求解描述流体运动的质量守恒方程、动量守恒方程和能量守恒方程,对复杂的流体流动进行数值模拟和系统分析。通过CFD数值模拟,可以方便地得到复杂流场内不同位置、不同时刻的基本物理量(如温度、速度、压力、浓度等)的数值和变化情况。本论文中采用目前功能最全面、使用最广泛的CFD软件—Fluent进行模拟计算。本论文通过使用Fluent软件模拟大水深水库温度分层、水深对扬水曝气器外围流场的影响,得到以下主要结论：(1)温度分层对于扬水曝气器稳定工作后形成除藻区域所占比例影响不大,无论夏季还是冬季工况,除藻区域所占比例基本稳定在75%左右。水库表层与底部温差大时,流场中漩涡的形成所需时间会比较长。当水库表层与底部温差相同时,斜温层的位置越深,流场中漩涡中心就越靠近水库底部。(2)在同样的作用半径、气弹周期和出口流速条件下,扬水曝气器工作时在大水深时形成稳定流场所需时间会大大增大,但在稳定的流场中除藻区域分布形式大致相同,除藻区域所占比例也基本相同。(3)利用Fluent的绘制质点迹线功能,可分析藻类在扬水曝气器稳定工作形成的流场中流动情况。藻类随漩涡流动,其在无光的衰亡区域流行时间远大于在生产区域的流行时间,经多次循环,藻类不断消耗自身的有机质,最终死亡。模拟结果表明扬水曝气器对藻类生长有抑制作用。(4)水深增大,藻类在无光的衰亡区域流行时间会增大,扬水曝气器的除藻效率会提高。但同时曝气器出口流动对流场的搅动作用就会相应降低,而且,大水深时产生气弹要克服的阻力大,扬水曝气器工作时所需动力就会增大,扬水曝气器的运行费用会增高。因此,宜综合考虑除藻效率和运行成本来选择扬水曝气器的布置地点。更多还原

【Abstract】 The Ware-lifting Aerator, aiming at solving water quality problems of eutrophication and pollutants’releasing from sediments in deep reservoirs, is a new water quality improvement device. By mixing water or oxygenating water directly, the aerator can improve and change the anaerobic state in the lower waters, which can control the pollutants’(such as nitrogen, phosphorus, iron, manganese, organic materials) releasing from sediment into the water body. By aerating, the waters in the upper-layer and lower-layer can be mixed, the thermal stratification can be destructed, and algae can then be brought down to the lower-layer where algae would die finally because of no light.With the help of the discretization method and the computer, the continuous equation, momentum equation and energy equation can be solved by Computational Fluid Dynamics (CFD) simulation, and complex flow motion can be numerically simulated and analysed. Using CFD simulation, the basic physical parameters (such as temperature, velocity, pressure, concentration) can be easily predicted at different locations and times. As a powerful computing package, FLUENT was employed to simulate the complex motions of air and water.Through the Fluent simulation, the effects of thermal stratification and water depth on the flow field around Water-lifting Aerator were investigated and the main conclusions were as follows:(1) Whether in the summer or winter, thermal stratification had little effect on the area without algae when the aerator worked stably, and the proportion of area without algae retained about 75%. If the temperature difference between the surface and bottom of the reservoir was noticeable, the time of developing the eddy zone was long. If the temperatures on the surface and bottom of the reservoir were the same, the deeper the thermocline layer, the nearer the eddy zone to the reservoir bottom.(2)Under the same conditions of affecting radius, gas shell period and outflow velocity, the time for steady flow development was long when the Water-lifting Aerator worked under the deep water condition. However, the proportions of area without area retained same.(3)Using Fluent’s function of tracing flow, the algae motion in the reservoir can be analyzed when the water-lifting aerator worked stably. Gong with the water flow, algae stayed in the decay area longer than in the production area. After several times of circulation, algae continued to consume their own organic materials and died ultimately.(4)If the water depth increases, the time of algae’s flowing through the decay area will increase, algae removal efficiency will increase. However, the stirring effect of outlet flow will be weakened accordingly, larger flow resistance will be overcome to develop gas shells, more energy will be required and the Water-lifting Aerator’s running costs will be higher. Therefore, comprehensive consideration of algae removal efficiency and operating costs should be given to select the optimum layout of the Water-lifting Aerator in the reservoir.更多还原