【作者】 杨丽丽；

【导师】 王晓玲；

【作者基本信息】 天津大学 ， 环境工程， 2007， 硕士

【摘要】 二沉池的设计主要是基于理想沉淀池的假设,确定二沉池的尺寸有很大的经验性、主观性和任意性。为此,有必要对二沉池内的流态和悬浮物浓度分布进行研究,从而比较精确的确定二沉池的尺寸和沉淀效率,以期为二沉池的设计和运行管理提供参考依据。在国内外已有的研究基础上,本文首先建立了三维Euler两相流模型。模型中将颗粒作为拟流体,采用改进的高雷诺数k -ε湍流模型,并在固相的湍流模拟中引入响应函数。该模型充分考虑了固液两相间相互作用的影响,即计入了相间曳力、横向升力、虚拟质量力和分散相体积分数以及分散相与连续相间密度差的影响;其次建立了二沉池三维拟单相流模型,并模拟了一定入水条件下的不同二沉池尺寸下水流和悬浮物分布。采用有限体积法中的PISO算法对平流式二沉池内流体三维流动过程进行了计算,并通过与Imam的实验结果进行比较,验证了数值模拟求解的正确性。模拟结果表明:(1)进水口下方和污泥斗上方存在回流区;二沉池内速度分布是非均匀的;其中宽度方向顶部水流由中心面分别向两边壁流动,底部水流流向中心面,中心面上速度较小,高速区主要分布在二沉池前部,靠近顶部以及污泥斗的前端。(2)进口挡板附近存在一较周围悬浮物浓度高的浓度区;在二沉池中部,由于悬浮物向顶部流动,底部悬浮物浓度较顶部低;污泥斗内悬浮物浓度较高。(3)进水区水流湍动能较大,而沉淀区内很小,出水口附近湍动能增大。(4)在一定入流条件下,二沉池挡板长度、位置对二沉池的流场和浓度场产生一定的影响;在悬浮物浓度不高的情况下,悬浮物颗粒尺寸对流场的影响并不明显,但影响了悬浮物在二沉池内的分布。(5)通过模拟不同二沉池尺寸下入流条件一定时的水流和悬浮物分布,拟合了悬浮物去除率与二沉池长、宽、高之间的函数关系。更多还原

【Abstract】 The design of secondary sedimentation tanks was based on the hypothesis of ideal sedimentation tanks, so it would depend greatly on empiricism, subjectivity and arbitrariness. It is necessary to study the flow field and the distribution of suspended solid concentration in the sedimentation tanks, and then the size and sedimentary efficiency of the tank could be determined more accurately. They would provide useful references for the design and operation management of the sedimentation tank.Firstly, based on the present research all over the world, a three-dimensional Euler two-phase flow model is built. The solid phase is treated as pseudo fluid in the model, which is coupled with particular high Reynolds number form of the k -εmodel. And the response function is introduced into the turbulence model of solid phase. The influence of interaction between liquid and solid, that is to say, the influence of interphase drag force, lifting force perpendicular to the relative velocity, virtual mass force, as well as the volume fraction of suspended solids and density difference effects between liquid and solid, has been considered. Secondly, a three-dimensional quasi-single phase model is built in the secondary sedimentation tank. Then the distributions of flow and suspended solids in different dimensions of the tanks under the specific inlet condition are simulated.The PISO algorithm of the finite volume method is used to compute the three-dimensional mathematics model. Good agreement is obtained between present CFD predictions and published experimental data of Imam. The simulated results are as follows:(1) The circumfluence areas are under the inlet and over the sludge hopper. The distribution of velocity is not uniform. The current along z-axis in the upper part of tank flows direct to the sidewalls from the center plane and reverses in the bottom, and the velocity value of the center plane is relatively small. The high-speed regions are mainly near the upper part of the tank and in the front of sludge hopper, which are in the front of the tank.(2) Higher concentration area is near the baffles of inlet. In the central region of the tank, due to flowing toward the surface of the tank, the concentration of suspended solid near the bottom is lower than the top. A large amount of suspended solid settles in the sludge hopper.(3) The turbulent kinetic energy of flow is high in the influent zone, while in the settling zone relatively low, and it increases near the outlet.(4) Under the specific inlet condition, the length and location of baffle have some effect on the flow field and concentration field in the sedimentation tank, while the dimension of suspension granule may not affect on the flow field, but influences the distribution of suspended solid in the tank.(5) Under the specific inlet condition, the function between the removal efficiency of suspended solid and the length, width and height of the tank is gained by simulating the distributions of flow and suspended solid in different dimensions of the tanks.更多还原