Numerical modeling method on the movement of water flow and suspended solids in two-dimensional sedimentation tanks in the wastewater treatment plant

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污水厂二维沉淀池水流和悬浮物运动数值模拟

以典型城市污水处理厂平流矩形沉淀池速度和浓度分布计算为例,利用涡量-流函数法建立控制方程,并以有限差分法中的控制容积法对方程进行了离散,求出速度分布场后,利用二维浓度迁移方程对沉淀池浓度分布进行了计算.通过与实验数据的对比,验证了方法的有效性与可行性.另外还对沉淀池数值模拟的应用进行了初步探索.     

数值模拟方法在二维沉淀池优化设计中的应用

简要介绍了数值方法在沉淀池悬浮物浓度计算中的应用方法 ,并尝试通过数值模拟过程建立起沉淀池沉降效率与几何尺寸间的关系 ,将其作为约束条件之一建立了一个简单的沉淀池优化设计模型。最后通过实例阐明了这种基于数值计算的优化设计模型的可行性和优势     

露天矿高陡边坡落石防护墙设计研究

将落石灾害防治研究引入到露天矿高陡边坡,结合河南省洛钼集团矿山公司某边坡落石问题进行模拟研究:首先采用动力学方法分析了落石运动轨迹的影响因素和运动方程,指明了落石防护设计的依据;然后采用数值模拟方法选取50块落石进行随机测试,重点考察落石的落点分布范围、弹跳高度和总动能等要素,以此为基础并结合边坡实际条件,设计了三道防护墙拦截落石的方案;最后确定了各道防护墙的位置、高度以及最小抗冲击强度.研究结果表明,该方案对落石的拦截率达到100%,对露天矿高陡边坡落石灾害的有效防治具有重要意义.     

Direct numerical simulation of the motion of circular pollutant particles in Newtonian fluid

An improved implementation of distributed multiplier/fictitious domain method is presented for the direct numerical simulation of particulate flow. The key improvement is to replace a finite-element triangulation for the velocity and a “twice-coarser“ triangulation for the pressure with a rectangular discretization for the velocity and pressure. For code validation, the sedimentation of a single particle in a twodimensional channel was simulated. The results showed that the simulation is independent of the mesh size as well as the time step. The comparison between experimental data and this simulation showed that our code can give a more accurate simulation on the motion of particlesthan previous DLM code. The code was then applied to simulate the sedimentation of 600 particles in a rectangular box. The falling course ispresented and discussed. At the same time, this simulation also demonstrates that the method presented in this paper can be used for solving the initial problems involving a lager number of particles exaclly with computing durations kept at acceptable levels.     

Numerical simulation of a horizontal sedimentation tank considering sludge recirculation

Most research conducted on the concentration distribution of sediment in the sedimentation tank does not consider the role of the suction dredge. To analyze concentration distribution more accurately, a suspended sediment transportation model was constructed and the velocity field in the sedimentation tank was determined based on the influence of the suction dredge. An application model was then used to analyze the concentration distribution in the sedimentation tank when the suction dredge was fixed, with results showing that distribution was in accordance with theoretical analysis. The simulated value of the outlet concentration was similar to the experimental value, and the trends of the isoconcentration distribution curves, as well as the vertical distribution curves of the five monitoring sections acquired through simulations, were almost the same as curves acquired through experimentation. The di erences between the simulated values and the experimental values were significant.     

基于不同配风方式下的四角切圆燃煤锅炉燃烧特性的数值计算研究

利用数值计算方法分析了某火电厂四角切圆燃煤锅炉炉内燃烧特性,重点考察了配风调整对炉内温度场、速度场、组分场、NO_x以及飞灰含碳量的影响规律。结果表明:不同配风方式下,炉内温度场和速度场的分布都比较合理,没有出现贴壁燃烧现象,倒宝塔配风时,炉膛出口CO的浓度和飞灰含碳量相比均等配风和正宝塔配风时要高,而NO_x浓度相比其他两种方式时要低。该研究结果可为四角切圆燃煤锅炉的实际运行提供了一定的参考。     

基于数值仿真-响应表面法的二沉池优化研究

以长沙市某污水处理厂二沉池为例,采用多相流混合物模型与k-ε湍流模型结合对辐流式二沉池内速度场和污泥浓度场进行了数值模拟.以出水口悬浮物浓度(SS)为响应目标,对影响二沉池沉淀效果的3个影响因素(进水口流速、颗粒污泥粒径、挡板的淹没深度)进行中心复合设计(central composite design,CCD),并经响应表面法分析得到影响出水SS的二次回归模型,确定了二沉池沉降的最佳条件:进水口流速为0.03m·s-1,颗粒污泥粒径为220.41μm,挡板的淹没深度为3.45m,采用数值仿真模拟实验得到出水口悬浮物浓度值为2.4mg·L-1,较优化之前的仿真结果一周平均值6.7mg·L-1相比,其处理效率提高了64.2%.采用数值仿真和响应表面法结合对二沉池工艺条件进行优化研究,可以加速寻优过程,是工艺优化的辅助工具.     

山体对烟羽弥散影响的一种数值模拟方法

本文对山地和丘陵地区中烟羽浓度扩散分布的计算提出一种方法,该方法引用浓度方程的分析解,通过对山地绕流数值计算速度势和流函数,可较简易地求得烟羽浓度分布。作为算例,文中对中条山某工厂烟囟排放的SO2,预测了它在各种风速时被输运扩敢的浓度分布。      

沉淀池的数值模拟

运用计算流体力学软件FLUENT模拟了平流式沉淀池在不同进水口高度,进水挡板位置,颗粒密度和圆弧形扰流板位置下的流场、悬浮物的浓度场。从模拟结果的分析比较可以看出,在一定范围内改变沉淀池的进水口高度,对沉淀池的去除效果没有影响。挡板的淹没深度和颗粒的密度则对悬浮物的去除效率影响较大。挡板的水平位置只在一定范围内变化才能使沉淀池保持较为理想的去除效率。圆弧形扰流板的加设可以改变沉淀池内流态不均的现象,从而提高沉淀池的运行效率。     

条缝型空气幕对抽油烟机污染控制的辅助作用

运用数值模拟和实验测试方法,研究了住宅厨房在油烟机和送风气幕作用下的气流流动、温度分布和污染物扩散机理,并通过CFD数值计算对比分析了射速在0~5m/s范围的空气幕对厨房污染物扩散的影响.结果表明,单独使用抽油烟机作为厨房排风系统无法有效地将烹饪产生的油烟快速排向室外.空气幕作为补风装置应用在厨房通风系统不仅可以降低厨房空气温度,提高人体热舒适,而且能合理组织气流流动,降低厨房污染物浓度.然而,当油烟机排风量一定时,空气幕射速并非与油烟机捕集效率成正比,而是存在着最佳设计风速,排风速率为5m/s的最佳空气幕射速为0.6m/s.当通过增加油烟机排风量来提高捕集效率时,应根据不同的排风量确认对应的空气幕射速.     

新型波纹板导流墙氧化沟水力特性的数值模拟

提出新型波纹板导流墙氧化沟结构,并基于N-S方程和k-ε紊流模型,采用有限体积法,对新型波纹板导流墙氧化沟的水流流态和水流速度分布进行数值模拟。同时与无延长导流墙和平板导流墙的数值模拟进行比较,研究结果表明:新型波纹板导流墙对降低氧化沟隔墙背后的水流低速区范围和改善污泥沉积有促进作用。     

Study on the wind field and pollutant dispersion in street canyons using a stable numerical method

A stable finite element method for the time dependent Navier-Stokes equations was used for studying the wind flow and pollutant dispersion within street canyons. A three-step fractional method was used to solve the velocity field and the pressure field separately from the governing equations. The Streamline Upwind Petrov-Galerkin(SUPG) method was used to get stable numerical results. Numerical oscillation was minimized and satisfactory results can be obtained for flows at high Reynolds numbers. Simulating the flow over a square cylinder within a wide range of Reynolds numbers validates the wind field model. The Strouhal numbers obtained from the numerical simulation had a good agreement with those obtained from experiment. The wind field model developed in the present study is applied to simulate more complex flow phenomena in street canyons with two different building configurations. The results indicated that the flow at rooftop of buildings might not be assumed parallel to the ground as some numerical modelers did. A counter-clockwise rotating vortex may be found in street canyons with an inflow from the left to right. In addition, increasing building height can increase velocity fluctuations in the street canyon under certain circumstances, which facilitate pollutant dispersion. At high Reynolds numbers, the flow regimes in street canyons do not change with inflow velocity.     

某钼矿尾矿库地下水污染的随机模拟

为分析参数不确定性对地下水污染数值模拟模型输出结果的影响,以某钼矿尾矿库地下水污染问题作为研究实例,选取钼离子作为模拟因子,建立该钼矿尾矿库地下水污染数值模拟模型,对输出结果进行不确定性分析.为降低替代模型的维数,运用灵敏度分析法筛选出对模拟模型输出结果影响较大的2个参数作为模型中的随机参数.为减少反复调用数值模拟模型产生的计算负荷,分别运用克里格方法和支持向量机法建立模拟模型的替代模型,并比较二者的精度,选择精度较高的替代模型完成蒙特卡罗随机模拟.最后,对随机模拟的输出结果进行统计分析与区间估计,对地下水污染超标的风险进行评价.结果表明：置信度为80%时,井1,2,3浓度值的置信区间分别为0.71~2.29,0.28~1.02,1.55~3.25mg/L.此外,结合《地下水质量标准》以及污染物浓度分布函数曲线,井1,2,3中水质达到地下水质量标准Ⅴ类的概率分别为99.7%,97.1%,99.6%.本研究可为地下水污染防治提供更科学、全面的参考依据.     

舟山高浊度海水混凝除浊研究

测定了舟山高浊度海水悬浮物的粒度分布,分析了高浊度海水自由沉降特性,选用氯化铁(FeCl)3、聚合氯化铁(PFC)、聚合硫酸铁(PFS)3种混凝剂,利用正交试验方法对高浊度海水进行混凝沉淀对比试验,采用极差分析方法研究了影响混凝效果的因素。试验结果表明:舟山海域悬浮物组成以粉砂为主,用自然沉降的方法是很难去除;各因素对浊度去除率影响的主次顺序均为:慢搅时间>慢搅速度>快搅时间>快搅速度;对于高浊度海水混凝除浊最佳水力条件为:快搅时间为2 min,快搅速度为300 r/min,慢搅时间为15 min,慢搅速度为60 r/min;聚合硫酸铁是较理想的絮凝剂,最佳投药量范围在15～25 mg/L,对浊度去除率高达99%以上。     

Numerical simulation of the sedimentation of cylindrical pollutant particles in fluid

The sedimentation of cylindrical pollutant particles which fall through a fluid is investigated. Differing from previous research work,particle oscillation and effect of particle on the fluid are considered, and the torque exerted on a particle when viscous fluid flow around a particle is got through experiment and included in the numerical simulation. The computational results showed that the sedimentation velocities of particle increase slowly with the increase of particle aspect ratio 9. For disk-like particle, when the motion direction of particle is parallel to axis of particle, particle falls more slowly than the case of perpendicular to axis of particle; while for rod-like particle, it is inverse. For sedimentation of a crowd of high-frequency oscillating cylindrical particles with arbitrary initial orientation, both vertical velocity and horizontal velocity oscillate dramatically, the degree of oscillation of the former is stronger than the later. A crowd of particles fall more quickly than an isolated particle. Particles tend to strongly align in the direction of gravity. The computational results agreed well with the experimental ones and helpful for controlling of pollutant particles.     

屋顶形状对街道峡谷内污染物扩散的影响

采用Spalart-Allmaras湍流模型,通过求解二维连续性方程,Navier-Stokes方程及污染物输运方程,模拟了具有不同屋顶形状的街道峡谷的流场及交通污染物浓度场.计算结果与风洞试验结果总体趋势一致.由于屋顶形状的不同,峡谷内的流场会形成顺时针或逆时针方向的旋涡,从而影响建筑物迎风面与背风面污染物浓度分布.在各种屋顶形状的街道峡谷中,壁面污染物浓度的相对大小与其附近的速度分布有直接关系.通过对街道峡谷建筑屋顶高度处垂直方向污染物通量的计算和比较,说明了不同屋顶形状的街道峡谷平均流扩散和湍流扩散的强弱,污染物湍流扩散通量值有可能为正或为负;同时,峡谷内剩余污染物浓度的大小表明了屋顶形状对污染物扩散出街道峡谷难易的影响.      

通风管道内负离子传输的数值模拟及试验验证

为能有效去除通风管道系统内颗粒及气溶胶微生物,解决通风空调系统因长期使用而缺少维护和清洁,造成气溶胶微生物在系统里滋生进而形成对人体有害的生物气溶胶病原体细菌等问题,采用欧拉方法建立模拟通风管道内负离子输运过程及分布的数值模型.通过数值模拟和试验测量VI-2500型负离子发生器安装在0.2 m×0.2 m通风管道内送风速度为3～6 m/s时的负离子浓度,验证数值模型的准确性并分析负离子在通风管道内的分布规律.结果表明,负离子的模拟预测值与试验测量值误差很小.送风速度为3 m/s时,风管内负离子浓度的最低值和平均值分别为9.15×109和2.39×109 ions/m3,送风速度为6 m/s时,相应为2.37×1010和6.83×109 ions/m3.通风管道内负离子浓度随送风速度的增加而升高,送风速度一定时,通风管道内负离子浓度沿风速方向逐渐降低.当送风速度低至3 m/s时,风管内负离子浓度最低或平均值仍然可以达到有效净化细菌的负离子浓度最低数量级的推荐值(108～1010 ions/m3).研究显示,负离子数值模型能准确预测VI-2500型负离子发生器在0.2 m×0.2 m风管中产生的负离子浓度,并且发生器产生的负离子浓度能满足4.5 m长风管的净化要求.      

Application of numerical simulation on optimum design of two-dimensional sedimentation tanks in the wastewater treatment plant

The paper establishes the relationship between the sttling efficiency and the sizes of the sedimentation through the process of numerical simulation,which is taken as of the constraints to set up a simple optimum dsigning model of sedimentation tank.The feasibility and advantages of this model based on numerical calculation are verified through the application of practical case.     

污泥动态沉降试验研究

在污泥静态沉降基础上,改进试验装置,对污泥沉降性能进行动态模拟。研究表明沉淀柱中上升流速小于5m/h时,污泥有较好的浓缩效果。试验结果对二沉池设计和污水厂改造有一定的指导作用。