鼓泡塔内气液两相流动力特性数值模拟研究

利用CFD软件模拟的方法研究鼓泡塔内气液两相流动力特性,为鼓泡塔的设计提供依据。采用欧拉-欧拉双流体模型分别结合标准k-ε紊流模型和RNG k-ε紊流模型对鼓泡塔内气液两相流进行数值模拟,并使用Phase Coupled SIMPLE算法进行速度与压力耦合求解。比较鼓泡塔内轴截面(y=0)处不同高度液相速度和气相速度的变化情况,发现速度沿径向呈现出抛物线分布,沿水深方向越接近通气孔,速度越大,且气相速度整体大于液相速度。通过将z=0.28 m处的垂向液相速度与实验值比较,得出欧拉-欧拉双流体模型结合标准k-ε紊流模型模拟鼓泡塔气液两相流动力特性优于RNG k-ε模型,且发现上升力对模拟结果有显著的影响。     

曝气池中气液两相流速度场分布的实验研究与数值模拟

气液两相流广泛存在于水利工程、废水处理等领域,其在气液装置中的流型流态及速度场分布可直接影响装置运行效能。本文采用实验研究与数值模拟相结合的方法,对圆柱形气液装置进行PIV实验,获得了准确的气液两相流气相速度场分布;在充分考虑湍流、曳力、升力、湍流分散力等作用下,采用欧拉-欧拉双流体模型和气泡群平衡模型对气液两相流流场进行了数值模拟,并将模拟结果与实验结果进行验证,所得结果误差控制在10%左右。结果表明,本文提出的模拟方法在气液两相流模拟中能够得到较准确的两相流动规律和速度场分布情况。     

生物倍增反应器气泡流态特性分析

利用激光粒子图像测速技术(PIV)对生物倍增反应器在7种不同进水流量下的气泡流态特性进行了测量和分析,利用特征正交分解方法对所测2个截面的气泡流场进行分解,提取流场中含能大尺度结构。结果表明, 进水流量的增加导致了气泡轴向速度减小,径向速度增大,气泡附壁效应增强;不同进水流量对气泡的扰流影响程度不同,气泡流态的速度场和涡量面积分布存在差异,在特定工况下气泡流场产生了涡旋。上部区域进水流量为0时,1阶模态占能比例最高,约为7.2%;下部区域进水流量为0.18 m3/h时,1阶模态占能比例最高,约为4.5%。低阶特征模态中存在明显的大尺度结构,且大尺度的流动结构与液相混合行为间接相关。当进水流量为0.90 m3/h时,2个截面的涡量面积分布最均匀,气泡死区最少,此时气泡流态最佳。在本试验条件下,进水流量为0.90 m3/h时,反应器整体气泡流态最佳。     

长江河口河槽水沙特性及其输移机制研究

基于2007年1、7月长江口大潮实测流速及悬沙量资料,运用数据统计和机制分解法分析各河槽水沙输移特性,结果表明:枯季优势流小于洪季,枯季北支、南支北侧、北港中下段、南槽南边滩为涨潮优势,其他河槽为落潮优势,洪季北槽口外为涨潮优势,其他河槽为落潮优势;悬沙输移主要驱动力为欧拉余流、潮泵效应、垂向环流和斯托克斯余流,欧拉余流在平流输沙中占主导地位,潮泵效应在潮流输沙中占主导地位,欧拉余流指向海,垂向环流和斯托克斯余流指向陆,潮泵效应除北港口外、南槽口外随季节变化外其余河槽指向海;不同汊道各输沙项的贡献随径流与潮汐潮流的相对重要性而变化。     

曝气池中气液两相流数值模拟

应用数值模拟的方法,对曝气池气液两相流运动规律进行了探讨。研究表明:当孔径相同,空气流量越大,紊动强度越大,气液混合越充分,曝气效果越好。对于相同的水深和相同的孔径,流量是影响气泡大小和速度的主要因素。当气体流量或速度增加时,气泡体积增大,气相速度也明显增大。     

基于改进箱体模型的赤潮水动力学模拟研究

针对甲藻能够主动垂向移动的特点,将传统一维箱体模型修正成7层垂向结构,增加拉格朗日粒子在不同层之间的质量交换模拟甲藻的垂向移动,使用欧拉方法模拟水体中其余环境变量的变化,研究赤潮发生期间甲藻的垂向移动和水体中溶解氧浓度变化之间的关系。以香港吉奥湾为例,对2001年多纹膝沟甲藻赤潮进行了模拟分析;以叶绿素a和溶解氧两个指标对模型进行验证。结果表明:叶绿素a和溶解氧的垂向浓度分布的模拟值和实测值基本符合;赤潮期间甲藻发生明显的垂向迁移,其呼吸、生长速率有所增加,水体中溶解氧浓度迅速下降。对传统箱体模型的垂向分层有助于了解赤潮期间水体垂向上微生物和溶解氧分布的差异,为进一步研究赤潮发生机制提供了参考依据。     

搅拌槽内流体力学特性的数值模拟研究

采用FLUENT6.3.26软件求解气液两相流,自由液面的捕捉采用VOF(volume of fluid)法,辅以标准k-ε湍流模型数值求解气液两相流时均方程,使用了半隐式SIMPLE(Semi-Implicit Method for Pressure-Linked Equations)算法求解速度与压力耦合方程组,旨在研究搅拌槽在搅拌过程中流体流动的力学特性,分析比较了不同水深处的水流沿半径方向的径向速度、切向速度及轴向速度的规律,经过研究和分析发现模拟的速度值与实验值吻合良好,为搅拌槽的设计和运行提供了参考。     

不同压力梯度平面库埃特流中扰动涡动力学特性

该文以不同压力梯度的平面库埃特流动为基本流,在壁面上构建一个局部微振荡射流扰动,利用直接数值模拟的方法求解三维不可压缩N-S方程,模拟了扰动涡结构的生成与演化过程。模拟结果表明:由于压力梯度的差异,虽然射流扰动期间的扰动涡幅值几乎相同,但幅值在不同的平面库埃特基本流中的演化特性表现出明显的差异;在相同时刻,库埃特基本流压力梯度越大,扰动涡的幅值越大,扰动控制方程中的基本流近壁速度梯度与扰动涡法向速度乘积项对幅值的增长起着主要作用;在不断增长的扰动涡中,呈现高速、低速条纹间隔密集的特性,由于扰动涡的存在,流动区域的近壁面平均切应力系数增加,在增长相对迅速的P??1时的库埃特基本流中形成了相对完整的发卡涡形态的涡量分布。     

射流元件附壁与切换流动规律研究

射流元件是射流式井底增压器的换向控制部件，元件内部射流具有稳定附壁和快速换向的特性。文中运用计算流体力学方法，数值模拟了射流元件内部射流稳定附壁与切换的流动过程。通过背压和控制流对射流附壁与切换过程影响规律的分析，揭示了射流元件流场附壁与切换的过程和机理，发现了控制流上游来流位置对射流附壁影响很大，可以通过合理选择信号道引流位置来增强附壁稳定性。研究结果对射流元件结构优化有指导意义。     

以叶轮起旋的气液两相螺旋流摩擦阻力特性实验研究

该文对以叶轮起旋的水平管内气液两相螺旋流的摩擦阻力压降特性进行了实验研究,水平实验管段为内径23 mm,长度为2 m的有机玻璃管,实验工质为空气和水,气相折算速度为0 m/s–3 m/s,液相折算速度为0 m/s–1.5 m/s。主要研究了流速以及叶轮参数对压降的影响,对比分析了气液两相非旋流与气液两相螺旋流的压降特点,实验结果表明:流体流速是管内摩擦阻力特性的重要影响因素,随着气相折算速度的增大,管内压降逐渐增大。叶轮参数对压降亦有较大影响,随着起旋角度的增大或者随着叶片面积的减小,压降均有逐渐变大的趋势。与气液两相非旋流相比,气液两相螺旋流的压降进一步增大;且随着气相折算流速的增加,螺旋流的压降增大速度要高于非旋流。最后,基于Lockhart和Martinelli方法,根据实验数据建立了气液两相螺旋流压降计算模型,研究结果表明理论值与实验测量值吻合较好。     

大石峡水电站进水口叠梁门分层取水试验研究

为分析电站进水口采用叠梁门型式分层取水方案的可行性,本文通过1：21.05的水工模型对大石峡水电站叠梁门分层取水进水口水力特性进行了系统研究。主要研究内容包括对不同叠梁门高度取水时,进水口的水流流态、叠梁门体的压力分布、叠梁门顶及竖向流道的流速分布、进水口段总的水头损失系数等。试验结果表明：电站进水口设置叠粱门后,叠梁门顶水头大于18.0 m时不产生有害吸气旋涡,门体压力分布接近静水压力分布;进水口段的水头损失在1.17~1.30 m之间;靠近叠梁门门顶部位的水流流速较大,表层水流流速较小;叠梁门后不同高程竖向流道的水流流速接近于梯形分布,主流偏于进水塔靠下游挡墙侧。在进水口设置叠梁门进行分层取水方案是可行的。     

The effect of bubble plume on oxygen transfer for moving bed biofilm reactor

The movement of the bubble plume plays an important role in the operation of a moving bed biofilm reactor （MBBR）, and it directly affects the contact and the mixture of the gas-liquid-solid phases in the aeration tank and also the oxygen transfer from the gas phase to the liquid phase. In this study, the velocity field is determined by a 4-frame PTV as well as the time-averaged and timedependent velocity distributions. The velocity distribution of the bubble plume is analyzed to evaluate the operating efficiency of the MBBR. The results show that the aeration rate is one of the main factors that sway the velocity distribution of the bubble plumes and affect the operating efficiency of the reactor.     

高水头船闸阀门顶缝空化切片试验研究

针对日益严峻的高水头单级船闸阀门顶缝空化问题,采用能够真实反映缝隙流特性的1:1切片模型试验,研究阀门顶缝空化特性及门楣自然通气防空化机理。研究表明,随着空化的发展,缝隙段依次发生喉口跌坎空化、主流中心空化和阀门面板空化,缝隙段负压区不断延伸,直至整个缝隙段达到稳定的-10 m水柱负压,压力脉动很小;门楣自然通气通过增加缝隙段压力,消除主流中心空化和阀门面板空化,抑制喉口跌坎空化。当采用门楣自然通气措施后,缝隙段压力稳定在-2 m水柱左右,空化消失,缝隙段水流脉动压力增大;缝隙段压力与单宽通气量近似二次多项式关系,通气量极值对应的缝隙段压力约-2 m水柱,此时缝隙段压力与通气量达到平衡状态,当缝隙段压力逐渐升高时,门楣通气量逐渐降低,直至自然通气停止。     

辐流式沉淀池液固两相流力学特性三维数值模拟

采用两相流混合模型,选取RNG k-ε湍流模型封闭两相流时均方程,对辐流式二次沉淀池液固两相流力学特性进行三维数值模拟。采用有限体积法求解微分方程;紊动能、紊流耗散均采用Quick离散格式;速度与压力耦合求解时使用了压力隐式算子分裂PISO(Pressure-Implicit with Splitting of Operators)算法。通过模拟获得了速度场、紊动能和污泥质量浓度等参量在空间的分布规律,对沉淀池的设计有一定的参考价值。     

A new side stream process for easily degradable industrial waste waters to avoid sludge bulking.

A new treatment scheme for the treatment of easily biodegradable industrial waste waters has been developed. The side stream treatment of dairy waste water with the excess sludge from the domestic treatment line of the regional treatment plant Bad V?slau has been operated successfully for a period of three years during which the industrial load stemming from the dairy increased from 800 kg COD/d to 2,500 kg COD/d with peak loads up to 5,000 kg/d. Despite of the increased load to the treatment plant the total aeration tank volume had not been increased. This treatment is performed in an existing aeration tank of the WWTP (V = 1,800 m3) which is now used as contact tank for the combined aeration of dairy waste water and excess sludge from the domestic treatment line (volume aeration tank = 15,000 m3). In this tank the easily degradable substrate from the industrial waste is mainly adsorbed to the biological sludge and after a mechanical dewatering transferred to the anaerobic digester where it yields in an increased gas production. The filtrate of the dewatering process is completely free from biodegradable material and can without danger of bulking be fed to the aeration tank of the domestic treatment line. The new process has proven to be extremely flexible since already now daily peak loads exceeding the design load by more then 60% could be treated in the plant without any problems. Compared to other alternatives for the dairy waste water treatment that were investigated during this study, the new side stream process is very advantageous. No other pre-treatment process for industrial waste water could have been operated under comparable loading conditions without severe operating problems.     

响水涧抽水蓄能电站引、尾水道上弯段弯道效应分析

分析研究响水涧抽水蓄能电站引水道、尾水道上弯段水力特性,明确其弯道效应主要表现形式为:门井边垂线流速大于或接近中垂线流速;中垂线流速分布呈轻微扭曲状;沿弯道(段)横断面圆周测压管水头不等于常数。试验表明:上弯段与门井间距离在5倍管径左右可以基本消除弯道效应对流速分布的影响,在7倍管径左右可以基本消除弯道效应对压力分布的影响。     

THE VELOCITY FIELD OF MULTIPHASE FLOW AND EFFICIENCY OF BIOLOGICAL AERATION FILTER

Aeration is an important factor affecting the biological aeration filter. With a set of experiment device specially designed for the purpose, and the particle image velocimetry technique, the velocity field of the gas-liquid two-phase flow is studied under different conditions. The various simulated aeration states were actually applied to the experimental device of sewage treatment, and the results of the numerical simulation were verified. The final experimental results indicate that the most efficient state occurs when the ratio of water in aeration tank h/w=1, the diameter of capillary tubes d=0.6mm and the velocity of bubbles v=0.3m/s.     

圆管流掺气减阻理论研究

本文研究了圆管中气液分层层流、分层紊流及掺气混合紊流情况下的阻力减小规律。理论研究表明，圆管中的气液分层层流、分层紊流，即在近壁层内充以空气，可以在相同的水流量下，使阻力下降，实现减阻。而掺气混合紊流时，只有当壁面附近的含气浓度大于圆管中心处的含气浓度时，才能在相同水流量下，使阻力下降，实现减阻     

不同孔眼数量下曝气池中气液两相流数值模拟

曝气池是活性污泥处理系统中的核心处理构筑物,而曝气池中气液两相分布及其流动规律对曝气作用的影响又至关重要。本文运用FLUENT软件对曝气池内气液两相流动问题进行了数值模拟,并对比了相同的曝气量,不同的孔眼数量下,曝气池内气液两相的分布情况和流动规律,说明了在本文所模拟的工况下采用孔眼数量为五孔时曝气效率最高。     

MEASUREMENT OF SOLID SLURRY FLOW VIA CORRELATION OF ELECTROMAGNETIC FLOW METER,ELECTRICAL RESISTANCE TOMOGRAPHY AND MECHANISTIC MODELLING

The study presented here was carried out to obtain the actual solids flow rate by the combination of electrical resistance tomography and electromagnetic flow meter. A new in-situ measurement method based on measurements of the Electromagnetic Flow Meters (EFM) and Electrical Resistance Tomography (ERT) to study the flow rates of individual phases in a vertical flow was proposed. The study was based on laboratory experiments that were carried out with a 50 mm vertical flow rig for a number of sand concentrations and different mixture velocities. A range of sand slurries with median particle size from 212 μm to 355 μm was tested. The solid concentration by volume covered was 5% and 15%, and the corresponding density of 5% was 1078 kg/m³ and of 15% was 1238 kg/m³. The flow velocity was between 1.5 m/s and 3.0 m/s. A total of 6 experimental tests were conducted. The equivalent liquid model was adopted to validate in-situ volumetric solids fraction and calculate the slip velocity. The results show that the ERT technique can be used in conjunction with an electromagnetic flow meter as a way of measurement of slurry flow rate in a vertical pipe flow. However it should be emphasized that the EFM results must be treated with reservation when the flow pattern at the EFM mounting position is a non-homogenous flow. The flow rate obtained by the EFM should be corrected considering the slip velocity and the flow pattern.