水下管道向下泄漏的羽/射流特性

对水下管道向下泄漏的羽流特性进行了实验及理论研究。采用拉格朗日控制体积分法建立了向下运动的羽动力模型,并对羽流参数进行了模拟。模拟结果表明模型对羽流半径及长度的预测与实验结果基本相符,但在接近羽流终端时,对羽流半径的预测结果要高于实验值。实验及模拟结果还表明,向下泄漏时羽流的初始动量衰减很快,与向上泄漏时羽流相比,羽流长度很短。随着Froude数的增大,向上羽流的长度增长较大,而向下羽流的长度却增长缓慢。     

水下管道向下泄漏的羽/射流特性

对水下管道向下泄漏的羽流特性进行了实验及理论研究。采用拉格朗日控制体积分法建立了向下运动的羽动力模型,并对羽流参数进行了模拟。模拟结果表明模型对羽流半径及长度的预测与实验结果基本相符,但在接近羽流终端时,对羽流半径的预测结果要高于实验值。实验及模拟结果还表明,向下泄漏时羽流的初始动量衰减很快,与向上泄漏时羽流相比,羽流长度很短。随着Froude数的增大,向上羽流的长度增长较大,而向下羽流的长度却增长缓慢。     

气泡羽流气液两相流动特性的研究进展

气泡羽流是一种复杂的气液两相流,广泛应用于废水处理、石油加工、环保等工业领域。气泡羽流的流动特性对气液两相间质量、动量传递及工业应用至关重要。本工作总结了理论与实验研究等方面气泡羽流流动特性的研究进展。详细讨论了气泡羽流气液两相流体水力学特性、羽流运动行为的影响因素。根据气含率、气泡直径等水力学参数的预测模型和经验公式,归纳了不同液相物性和结构参数下羽流模型的适用范围,揭示了流动对传质的作用。总结了分层流体中气泡羽流流型变化规律、羽流去分层效果以及引起流型变化的影响因素。阐释了横向流动环境下羽流的偏移行为呈线性变化,该变化与横向流速及表观气速等因素有关。最后讨论了气泡羽流气液两相流动特性研究手段和理论方法的局限性,展望了气泡羽流运动规律多尺度研究的方向。     

二维气雾两相射流锥内速度分布的计算和验证

结合单顶粒动力学模型与普朗特混合长度理论,对二维气雾两相射流体系中颗粒的时均速度和脉动速度进行了求解,结果表明颗粒在径向的轴向流速呈正态分布,射流轴收线附近紊动较强,随着射流向外发展,紊动逐渐降低,实验证明模型计算值与实验值吻合较好,能较好地体现二维气雾两相射流特性,具有一定的可行性和实用性。     

水下天然气管道泄漏扩散数值模拟

目前,对于水下天然气管道泄漏的研究相对较少,泄漏气体的扩散规律尚不明确,这给事故发生后的应急处理带来了很大的困难。建立水下管道泄漏二维模型,采用VOF多相流模型,通过模拟软件对不同水流速度下的天然气泄漏扩散过程进行数值模拟。结果显示:泄漏初期,气团聚集成球状,由于中部气团上升速度较快,气团变为月牙状,随后分裂为许多小气团四处飞散,随着水流速度的增加,泄漏气体浓度降低的更快,气团向右侧偏移距离增大。该研究对事故发生以后的危险区域划定有意义。     

气泡羽流摆动特性及附壁效应研究

针对气泡发生器中气泡在上升阶段发生的摆动现象会影响气泡生成效率的问题,利用流体体积函数(VOF)模型模拟了水槽内气泡生成和上升过程,研究了通气速度、气泡孔口直径和水槽高宽比对气泡羽流的影响,探究气泡的摆动特性和偏移程度。结果表明,气泡羽流摆动的最大偏移量与弗劳德数和水槽宽高比呈指数衰变关系;而最大偏移量对应的偏移角度与弗劳德数和水槽宽高比呈多项式关系。根据所得数据拟合得到相关经验关系式,给出了不同弗劳德数和水槽宽高比对应的气泡摆动特性的规律。     

CO2气泡群上升过程的CFD-PBM模拟

为揭示CO₂气泡群在方形鼓泡塔中上升过程的气液两相流行为，采用双流体模型耦合PBM(种群平衡方法)进行数值模拟，考虑气泡间的聚并和破碎现象，与部分实验结果相互对比，验证数值模型具有一定的可靠性，并分析入口气速、塔高宽比和入口分布器结构对气液流动情况、相含率和液相速度的影响，模拟结果表明：气泡群的上升过程出现了周期性的羽流震荡现象，改变气速会影响塔内气泡羽流的震荡程度；流动过程液相发生湍动，随着塔高宽比增大，液相循环模式实现了从“冷却塔”形式到“交错涡旋”的转变；不同入口结构下相含率分布有差异，大入口的震荡更早到来，但震荡持续时间较小入口结构短。研究CO₂气泡群的多相流动规律为鼓泡塔的设计和优化提供了理论参考。     

基于FTM方法的双气泡融合特性模拟

采用界面追踪法(FTM)对气泡融合现象进行数值模拟,将模拟结果与文献结果进行对比,验证了计算模型的准确性。结果表明,同轴双气泡上升速度均高于单独气泡的上升速度,且融合后气泡与等直径单气泡上升速度相同。气泡间距较小时,跟随气泡的上升速度更高。引导气泡的厄特沃什数Eo=0.36~9,Eo较大时两气泡上升阶段时间较短,但接触阶段时间较长,接触阶段气泡间的液膜在压力作用下逐渐变薄,最终破裂,气泡融合。Eo?4.16时,气泡融合所需时间随Eo增加而增加;Eo?4.16时,气泡融合所需时间不再变化。莫顿数Mo=0.57,Eo=5.04~18.72时,存在特定的双气泡初始角度?c,当0?≤?≤?c时,双气泡相互排斥;当?c≤?≤90?时,双气泡融合,且?c随Eo增加而降低.     

基于Fluent的海底原油管道溢油扩散特性研究

海底原油管道的泄漏会对自然生态系统带来巨大破坏,快速获得溢油扩散路径、油滴分布及泄漏浓度等参数对减少损失至关重要.基于此,利用计算流体力学软件Fluent建立二维有风模型对水下溢油行为规律进行研究,并将该模型模拟结果与ZHU的实验值对比证实了模型准确性.模型选用VOF方法(volume of fluid method),结合标准k-ε湍流方程,研究了溢油速度、破口尺寸、环境水深对溢油过程的影响.结果表明:随着溢油速度、破口尺寸的增大,相同时间内溢油扩散范围及海域内体积浓度增大,到达海平面时间减小.泄漏点处水深增大对溢油的扩散范围影响不大,但会延迟溢油达到海面的时间,降低海域内体积浓度.最后通过无量纲分析法给出不同工况下溢油横向漂移距离计算公式,为处理溢油事故提供可靠依据.     

竖直上升气液泡状流数学模型封闭的研究

竖直上升管气液两相流广泛应用于相变传热、核反应堆等工业过程。本文以竖直上升气液两相流为研究对象,运用欧拉双流体模型,针对表观液速为0.45m/s、表观气速分别为0.015m/s和0.1m/s的泡状流数值模拟过程中的升力、壁面润滑力、湍流扩散力、气泡诱导湍流（BIT）等封闭模型,开展数值模拟比较研究。模拟发现：①低气速泡状流中,升力和壁面润滑力的同时加入能够改善壁面附近的气含率,气泡在这两个力作用下在径向上达到一个相对平衡,得到与实验气含率类似的壁面峰,模拟的液相速度较合理;低气速时,BIT的影响可以忽略。②高气速泡状流中,BIT对气-液两相流的模拟结果影响比较明显,湍动耗散源项的加入能使液速分布的模拟结果得到改善,Troshko模型相对Sato模型更能反映气泡诱导湍流对液相湍流的作用。③高气速时升力的引入使气含率产生壁面峰,加入湍流扩散力能使峰值略微降低,但仍没有解决高气速时引入升力出现的气含率壁面峰问题,说明在径向上湍流扩散力还不足以抵抗升力。     

On the development of flow pattern in a bubble column reactor: Experiments and CFD

A comprehensive analysis of the development of flow pattern in a bubble column reactor is presented here through extensive LDA measurements and CFD predictions. In the LDA measurements, the simultaneous measurements of 2D velocity-time data were carried out at several radial locations and many axial cross-sections of the column for two different spargers. The profiles of mean axial liquid velocity, fractional gas hold-up and bubble slip velocity showed excellent agreement between the predictions and the experimentally measured values. The experimental results showed that the mean tangential velocity varies systematically in the radial as well as along the axial co-ordinates. The turbulence parameters viz. turbulent kinetic energy, energy dissipation rate and eddy diffusivity were also analysed. The estimated values of local energy dissipation rate obtained using eddy isolation model were used for establishing the energy balance in the column. The experimental data were used for the estimation of normal and shear stress profiles. For the case of single point sparger, just above the sparger region, the bubble plume was seen to have a strong tangential component of motion thereby yielding higher gas hold-up slightly away from the centre. This visual observation was well captured in profiles of all the hydrodynamic parameters obtained from the experimental data. CFD simulations of the mean velocities, gas hold-up and turbulent kinetic energy compared well with the experimental results.     

CFD simulation of bubbly flows: Random dispersion model

Three-dimensional CFD simulations of two-phase flow in a vertical pipe, a square cross-sectional bubble column and a large-scale plume are presented. A random dispersion model (RDM) is used to generate an instantaneous turbulent fluctuating velocity field by assuming that it is comprised of eddies, lifetimes and length-scales of which can be deduced from local mean flow properties. The RDM is used to describe turbulent dispersion of bubbles, and is validated here against the experimental data, and compared with predictions obtained by imposing an empirical turbulent dispersion force (TDF), but without introducing adjustable coefficients. The strictly mechanistic approach to bubble dispersion can offer better opportunities for the development of trustworthy, two-phase flow models.     

旋流板塔内气相流场的速度及压降的数值模拟

通过FLUENT计算流体力学软件对旋流板塔内的气相流场进行数值模拟分析。采用k-ε湍流模型和SIMPLER算法,对旋流板塔内气相流场进行三阶运算,得到气相流场的三维描述。模拟结果表明：将模拟所得的压降与试验值进行对比,发现在小进气量工况下数值模拟结果和试验结果吻合较好;在旋流板塔流场内部,存在一轴向速度为负的区域;切向速度随着高度的增加而强度减弱;径向速度随着高度的增加,减小的趋势比较明显。     

LOCAL HYDRODYNAMICS IN AN EXTERNAL LOOP AIRLIFT SLURRY REACTOR WITH AND WITHOUT A RESISTANCE-REGULATING ELEMENT

The hydrodynamic behavior of an external loop airlift slurry reactor (ALSR) with and without a resistance-regulating element was studied with a fiber optic probe and ultrasound Doppler velocimetry. The influences of the superficial gas velocity and solid holdup on the global gas holdup and radial profiles of the suspension circulation velocity in the downer and of gas holdup, bubble size, and bubble rise velocity in the riser were studied. Local measurements allow a better understanding of the flow behavior in the reactor and can be used for CFD modeling and validation. Experimental results show that the resistance-regulating element increases the gas holdup and decreases the suspension circulation velocity, indicating that an optimum design of the flow resistance is needed to obtain the maximum gas-liquid volumetric mass transfer coefficient for a specific superficial gas velocity. A high superficial gas velocity and low solid holdup are favorable for increased uniformity of the radial profile of the gas holdup and bubble rise velocity. Hydrodynamic models that predict the gas holdup and suspension circulation velocity were developed for an ALSR with and without a resistance-regulating element. Good agreement was obtained between measured and predicted values.     

湍动浆态床流体力学研究(Ⅴ)-带多层水平网格的浆态床流体力学模型

水平布置的多层筛网是最简单的阻尼型内构件,用于改善流动分布。在安装多层筛网的?500×5000鼓泡塔冷模装置中进行了流速分布与气含率分布测定。实验表明,网格型内构件可以有效抑制塔中心区过快上升的流速,改善其分布。网孔越小,流动阻尼效果越明显,同时平均气含率也会有所增大。提出了与列管内构件相似的一维流体力学模型,将网格内构件对流体的阻尼效果作为体积源来考虑,湍流耗散方程中的参数值c3=1.0,c4=1.3与列管束内构件略有不同。模型计算与实验数据符合良好,能够定量描述网格型阻尼内构件对流场的影响。     

LOCAL HYDRODYNAMICS IN AN EXTERNAL LOOP AIRLIFT SLURRY REACTOR WITH AND WITHOUT A RESISTANCE-REGULATING ELEMENT

The hydrodynamic behavior of an external loop airlift slurry reactor (ALSR) with and without a resistance-regulating element was studied with a fiber optic probe and ultrasound Doppler velocimetry. The influences of the superficial gas velocity and solid holdup on the global gas holdup and radial profiles of the suspension circulation velocity in the downer and of gas holdup, bubble size, and bubble rise velocity in the riser were studied. Local measurements allow a better understanding of the flow behavior in the reactor and can be used for CFD modeling and validation. Experimental results show that the resistance-regulating element increases the gas holdup and decreases the suspension circulation velocity, indicating that an optimum design of the flow resistance is needed to obtain the maximum gas-liquid volumetric mass transfer coefficient for a specific superficial gas velocity. A high superficial gas velocity and low solid holdup are favorable for increased uniformity of the radial profile of the gas holdup and bubble rise velocity. Hydrodynamic models that predict the gas holdup and suspension circulation velocity were developed for an ALSR with and without a resistance-regulating element. Good agreement was obtained between measured and predicted values.     

Dynamics of gas–liquid flow in a rectangular bubble column: experiments and single/multi-group CFD simulations

Several flow processes influence overall dynamics of gas–liquid flow and hence mixing and transport processes in bubble columns. In the present work, we have experimentally as well as computationally studied the effect of gas velocity, sparger design and coalescence suppressing additives on dynamics of gas–liquid flow in a rectangular bubble column. Wall pressure fluctuations were measured to characterize the low frequency oscillations of the meandering bubble plume. Bubble size distribution measurements were carried out using high-speed digital camera. Dispersed gas–liquid flow in bubble column was modelled using Eulerian–Eulerian approach. Bubble population was represented in the model with a single group or multiple groups. Bubble coalescence and break-up processes were included in the multi-group simulations via a suitable population balance framework. Effect of superficial gas velocity and sparger configurations was studied using single-group simulations. Model predictions were verified by comparison with the experimental data. Role of bubble size in determining plume oscillation period was studied. Multi-group simulations were carried out to examine evolution of bubble size distribution. An attempt is made to understand the relationship between local and global (over all the dispersion volume) bubble size distribution. The models and results reported here would be useful to develop and to extend the applications of multi-group CFD models.     

Hydrodynamics of turbulent slurry bubble column (Ⅳ)Modeling and simulation of bubble column with vertical pipe bundles

工业浆态床反应器一般都安装有密集的换热列管,列管束的存在使得速度和气含率的径向分布趋于陡峭,形成“烟囱效应”,目前对此还缺乏合适的流体力学模型进行定量描述。本文提出两点新思路以解决列管束的模拟问题：一是将密集列管束的影响作为体积源项而不是边界条件来考虑,在标准k-ε方程中增加与列管阻力相关的动量源、湍动源、耗散源本构关系;二是采用气泡群的径向升力和湍流扩散力平衡方程确定气含率径向分布。新模型中引入的阻力系数由流体力学文献给出,只有两个径向力和耗散参数需实验确定。模型计算的气含率和液速分布在宽泛的条件下与实验测量值符合良好,能够定量描述“烟囱效应”以及内构件参数对流动的影响。