第20章 通用多相流模型--60页 多相流数据后处理

多相流领域的数值计算方法及应用随着工业化和科技的不断进步，多相流领域的研究和应用越来越受到重视。

物料在流动过程中会与其他物料或界面发生相互作用，这种复杂的流动状况被称为多相流。

多相流涉及到固体、液体和气体等不同物态的介质，因此其研究和应用需要使用复杂的数值计算方法。

一、多相流的特点多相流的研究和应用过程中涉及到很多行业，比如化工、能源、航空航天等领域。

多相流介质的物理性质不同，具有以下几个特点：1. 相互作用强烈不同相态的物料之间会发生相互作用，例如固体微粒在液体中的漂浮、液滴在气体中的破裂等。

2. 物料运动混乱多相流介质的物料运动速度和方向较难预测，因此多相流的运动模式通常非常复杂。

3. 传递规律复杂多相流介质中不同物料的传递规律复杂，例如液滴的运动、未熔化固体在熔体中的运动等。

4. 可能存在相变多相流介质因为具有不同物态的物料，因此可能存在相变现象，例如气体在液体中的溶解等。

二、多相流的数值计算方法多相流的复杂性使得其研究和应用需要结合各种学科，比如计算流体力学（CFD）、材料科学、传热学等。

在多相流的计算过程中，有两个重要的假设：连续介质假设和相间界面模型。

1. 连续介质假设连续介质假设认为多相流介质可以像单相流一样，被视为连续的流体。

在这种假设下，物理量如质量、动量、能量等可以通过微分方程来描述，以求解其全场的运动学性质。

2. 相间界面模型多相流中不同相态物质的相互作用，使得相界面的存在成为一大难点。

通过相间界面模型对相变的过程和相界面的运动进行数值模拟，从而模拟多相流介质中不同物理量的分布和传递规律。

目前，常见的多相流计算方法包括欧拉方法、拉格朗日方法和欧拉-拉格朗日复合方法。

3. 欧拉方法欧拉方法模拟多相流介质中的物理量在时间和空间上的分布规律。

该方法将不同相态之间的相互作用描述为源项，通过物理量的守恒方程，来求解多相流介质内各物理量的分布规律。

4. 拉格朗日方法拉格朗日方法着重于对多相流介质中物体的运动轨迹进行跟踪和计算。

FLUENT多相流模型分类1、气液或液液流动气泡流动：连续流体中存在离散的气泡或液泡液滴流动：连续相为气相，其它相为液滴栓塞（泡状）流动：在连续流体中存在尺寸较大的气泡分层自由流动：由明显的分界面隔开的非混合流体流动。

2、气固两相流动粒子负载流动：连续气体流动中有离散的固体粒子气力输运：流动模式依赖，如固体载荷、雷诺数和例子属性等。

最典型的模式有沙子的流动，泥浆流，填充床以及各相同性流流化床：有一个盛有粒子的竖直圆筒构成，气体从一个分散器进入筒内，从床底不断冲入的气体使得颗粒得以悬浮。

3、液固两相流动泥浆流：流体中的大量颗粒流动。

颗粒的stokes数通常小于1。

大于1是成为流化了的液固流动。

水力运输：在连续流体中密布着固体颗粒沉降运动：在有一定高度的盛有液体的容器内，初始时刻均匀散布着颗粒物质，随后，流体会出现分层。

4、三相流以上各种情况的组合多相流动系统的实例气泡流：抽吸、通风、空气泵、气穴、蒸发、浮选、洗刷。

液滴流：抽吸、喷雾、燃烧室、低温泵、干燥机、蒸发、气冷、洗刷。

栓塞流：管道或容器中有大尺度气泡的流动分层流：分离器中的晃动、核反应装置沸腾和冷凝粒子负载流：旋风分离器、空气分类器、洗尘器、环境尘埃流动气力输运：水泥、谷粒和金属粉末的输运流化床：流化床反应器、循环流化床泥浆流：泥浆输运、矿物处理水力输运：矿物处理、生物医学、物理化学中的流体系统沉降流动：矿物处理。

多相流模型的选择原则1、基本原则1)对于体积分数小于10%的气泡、液滴和粒子负载流动，采用离散相模型。

2)对于离散相混合物或者单独的离散相体积率超出10%的气泡、液滴和粒子负载流动，采用混合模型或欧拉模型。

3)对于栓塞流、泡状流，采用VOF模型4)对于分层/自由面流动，采用VOF模型5)对于气动输运，均匀流动采用混合模型，粒子流采用欧拉模型。

6)对于流化床，采用欧拉模型7)泥浆和水力输运，采用混合模型或欧拉模型。

8)沉降采用欧拉模型9)对于更一般的，同时包含多种多相流模式的情况，应根据最感兴趣的流动特种，选择合适的流动模型。

多相流模型经验谈多相流的介绍：Currently there are two approaches for the numerical calculation of multiphase flows: the Euler-Lagrange approach and theEuler-Euler approach.The Euler-Lagrange Approach:The Lagrangian discrete phase model in FLUENT follows the Euler-Lagrange approach, this approachis inappropriate for the modeling of liquid-liquid mixtures, fluidized beds, or any application where the volume fractionof the second phase is not negligible.The Euler-Euler Approach: In FLUENT, three different Euler-Euler multiphase models are available: the volume of fluid (VOF)model, the mixture model, and the Eulerian model.1)The VOF Model: it is designed for two or more immiscible fluids where the position of the interface between the fluids isof interest. Applications of the VOF model include stratified flows, free-surface flows, filling, sloshing, the motion oflarge bubbles in a liquid, the motion of liquid after a dam break, the prediction of jet breakup (surface tension), and thesteady or transient tracking of any liquid-gas interface.2) Mixture model:Applications of the mixture model include particle-laden flows with low loading, bubbly flows, sedimentation,and cyclone separators. The mixture model can also be used without relative velocities for the dispersed phases to modelhomogeneous multiphase flow.3)Applications of the Eulerian multiphase model include bubble columns, risers, particle suspension, and fluidized beds.离散相模型（离散相的装载率10～12%）求解参数的设定：Options for Interaction with Continuous Phase：For steady-state simulations, increasing the Number of Continuous PhaseIterations per DPM Iteration will increase stability but require more iterations to converge.Update DPM Sources Every Flow Iteration is recommended when doing unsteady simulations; at every DPM Iteration, the particlesource terms are recalculated.Length Scale: controls the integration time step size used to integrate the equations of motion for the particle.A smallervalue for the Length Scale increases the accuracy of the trajectory and heat/mass transfer calculations for the discretephase.Length Scale factor: A larger value for the Step Length Factor decreases the discrete phase integration time step.颗粒积分方法：numerics叶中tracking scheme选项1）implicit uses an implicit Euler integration of Equation 23.2-1 which is unconditionally stable for all particle relaxationtimes.2）trapezoidal uses a semi-implicit trapezoidal integration.（梯形积分）3）analytic uses an analytical integration of Equation 23.2-1 where the forces are held constant during the integration.4）runge-kutta facilitates a 5th order Runge Kutta scheme derived by Cash and Karp [47].You can either choose a single tracking scheme, or switch between higher order and lower order tracking schemes using anautomated selection based on the accuracy to be achieved and the stability range of each scheme.Max. Refinements is the maximum number of step size refinements in one single integration step. If this number is exceededthe integration will be conducted with the last refined integration step size.Automated Tracking Scheme Selection provides a mechanism to switch in an automated fashion between numerically stable lowerorder schemes and higher order schemes, which are stable only in a limited range. In situations where the particle is farfrom hydrodynamic equilibrium, an accurate solution can be achieved very quickly with a higher order scheme, since theseschemes need less step refinements for a certain tolerance. When the particle reaches hydrodynamic equilibrium, the higherorder schemes become inefficient since their step length is limited to a stable range. In this case, the mechanism switchesto a stable lower order scheme and facilitates larger integration steps.Including a Coupled Heat-Mass Solution on the Particles：This increased accuracy, however, comes at the expense of increasedcomputational expense.非稳态跟踪1）连续相稳态离散相非稳态：you simply enter the Particle Time Step Size and the Number of Time Steps, thus tracking particlesevery time a DPM iteration is conducted. When you increase the Number of Time Steps, the droplets penetrate the domain faster.2）连续离散相都为非稳态：When solving unsteady equations for the continuous phase, you must decide whether you want to UseFluid Flow Time Step to inject the particles, or whether you prefer a Particle Time Step Size independent of the fluid flowtime step. With the latter option, you can use the Discrete Phase Model in combination with changes in the time step forthe continuous equations, as it is done when using adaptive flow time stepping.随机轨道模型的参数：number of tries:An input of zero tells FLUENT to compute the particle trajectory based on the mean continuous phase velocityfield (Equation 23.2-1), ignoring the effects of turbulence on the particle trajectories. An input of 1 or greater tellsFLUENT to include turbulent velocity fluctuations in the particle force balance as in Equation 23.2-20.If you want the characteristic lifetime of the eddy to be random (Equation 23.2-32), enable the Random Eddy Lifetime option.You will generally not need to change the Time Scale Constant (CL in Equation 23.2-23) from its default value of 0.15,unless you are using the Reynolds Stress turbulence model (RSM), in which case a value of 0.3 is recommended.液滴颗粒碰撞与破碎碰撞：破碎：有两种模型，TAB 模型适合低韦伯数射流雾化以及低速射流进入标态空气中的情况。

1.多相流动模式我们可以根据下面的原则对多相流分成四类：•气-液或者液-液两相流：o 气泡流动：连续流体中的气泡或者液泡。

o 液滴流动：连续气体中的离散流体液滴。

o 活塞流动: 在连续流体中的大的气泡o 分层自由面流动：由明显的分界面隔开的非混合流体流动。

•气-固两相流：o 充满粒子的流动：连续气体流动中有离散的固体粒子。

o 气动输运：流动模式依赖诸如固体载荷、雷诺数和粒子属性等因素。

最典型的模式有沙子的流动，泥浆流，填充床，以及各向同性流。

o 流化床：由一个盛有粒子的竖直圆筒构成，气体从一个分散器导入筒内。

从床底不断充入的气体使得颗粒得以悬浮。

改变气体的流量，就会有气泡不断的出现并穿过整个容器，从而使得颗粒在床内得到充分混合。

•液-固两相流o 泥浆流：流体中的颗粒输运。

液-固两相流的基本特征不同于液体中固体颗粒的流动。

在泥浆流中，Stokes 数通常小于1。

当Stokes数大于1 时，流动成为流化（fluidization）了的液-固流动。

o 水力运输: 在连续流体中密布着固体颗粒o 沉降运动: 在有一定高度的成有液体的容器内，初始时刻均匀散布着颗粒物质。

随后，流体将会分层，在容器底部因为颗粒的不断沉降并堆积形成了淤积层，在顶部出现了澄清层，里面没有颗粒物质，在中间则是沉降层，那里的粒子仍然在沉降。

在澄清层和沉降层中间，是一个清晰可辨的交界面。

•三相流 (上面各种情况的组合)各流动模式对应的例子如下：•气泡流例子：抽吸，通风，空气泵，气穴，蒸发，浮选，洗刷•液滴流例子：抽吸，喷雾，燃烧室，低温泵，干燥机，蒸发，气冷，刷洗•活塞流例子：管道或容器内有大尺度气泡的流动•分层自由面流动例子：分离器中的晃动，核反应装置中的沸腾和冷凝•粒子负载流动例子：旋风分离器，空气分类器，洗尘器，环境尘埃流动•风力输运例子：水泥、谷粒和金属粉末的输运•流化床例子：流化床反应器，循环流化床•泥浆流例子: 泥浆输运，矿物处理•水力输运例子：矿物处理，生物医学及物理化学中的流体系统•沉降例子：矿物处理2. 多相流模型FLUENT中描述两相流的两种方法:欧拉一欧拉法和欧拉一拉格朗日法，后面分别简称欧拉法和拉格朗日法。

20.通用多相流模型（General Multiphase Models）本章讨论了在FLUENT中可用的通用的多相流模型。

第18章提供了多相流模型的简要介绍。

第19章讨论了Lagrangian离散相模型，第21章讲述了FLUENT中的凝固和熔化模型。

20.1选择通用多相流模型（Choosing a General Multiphase Model）20.2VOF模型(Volume of Fluid(VOF)Model)20.3混合模型(Mixture Model)20.4欧拉模型(Eulerian Model)20.5气穴影响(Cavity Effects)20.6设置通用多相流问题(Setting Up a General Multiphase Problem)20.7通用多相流问题求解策略(Solution Strategies for General Multiphase Problems)20.8通用多相流问题后处理(Postprocessing for General Multiphase Problems)20.1选择通用的多相流模型（Choosing a General Multiphase Model）正如在Section 18.4中讨论过的，VOF模型适合于分层的或自由表面流，而mixture和Eulerian 模型适合于流动中有相混合或分离，或者分散相的volume fraction超过10%的情形。

（流动中分散相的volume fraction小于或等于10%时可使用第19章讨论过的离散相模型）。

为了在mixture模型和Eulerian模型之间作出选择，除了Section18.4中详细的指导外，你还应考虑以下几点：★如果分散相有着宽广的分布，mixture模型是最可取的。

如果分散相只集中在区域的一部分，你应当使用Eulerian模型。

★如果应用于你的系统的相间曳力规律是可利用的（either within FLUENT or through a user-defined function），Eulerian模型通常比mixture模型能给出更精确的结果。

多相流的介绍：Currently there are two approaches for the numerical calculation of multiphase flows: the Euler-Lagrange approach and theEuler-Euler approach.The Euler-Lagrange Approach:The Lagrangian discrete phase model in FLUENT follows the Euler-Lagrange approach, this approachis inappropriate for the modeling of liquid-liquid mixtures, fluidized beds, or any application where the volume fractionof the second phase is not negligible.The Euler-Euler Approach: In FLUENT, three different Euler-Euler multiphase models are available: the volume of fluid (VOF)model, the mixture model, and the Eulerian model.1)The VOF Model: it is designed for two or more immiscible fluids where the position of the interface between the fluids isof interest. Applications of the VOF model include stratified flows, free-surface flows, filling, sloshing, the motion oflarge bubbles in a liquid, the motion of liquid after a dam break, the prediction of jet breakup (surface tension), and thesteady or transient tracking of any liquid-gas interface.2) Mixture model:Applications of the mixture model include particle-laden flows with low loading, bubbly flows, sedimentation,and cyclone separators. The mixture model can also be used without relative velocities for the dispersed phases to modelhomogeneous multiphase flow.3)Applications of the Eulerian multiphase model include bubble columns, risers, particle suspension, and fluidized beds.离散相模型（离散相的装载率10～12%）求解参数的设定：Options for Interaction with Continuous Phase：For steady-state simulations, increasing the Number of Continuous PhaseIterations per DPM Iteration will increase stability but require more iterations to converge.Update DPM Sources Every Flow Iteration is recommended when doing unsteady simulations; at every DPM Iteration, the particlesource terms are recalculated.Length Scale: controls the integration time step size used to integrate the equations of motion for the particle.A smallervalue for the Length Scale increases the accuracy of the trajectory and heat/mass transfer calculations for the discretephase.Length Scale factor: A larger value for the Step Length Factor decreases the discrete phase integration time step.颗粒积分方法：numerics叶中tracking scheme选项1）implicit uses an implicit Euler integration of Equation 23.2-1 which is unconditionally stable for all particle relaxationtimes.2）trapezoidal uses a semi-implicit trapezoidal integration.（梯形积分）3）analytic uses an analytical integration of Equation 23.2-1 where the forces are held constant during the integration.4）runge-kutta facilitates a 5th order Runge Kutta scheme derived by Cash and Karp [47].You can either choose a single tracking scheme, or switch between higher order and lower order tracking schemes using anautomated selection based on the accuracy to be achieved and the stability range of each scheme.Max. Refinements is the maximum number of step size refinements in one single integration step. If this number is exceededthe integration will be conducted with the last refined integration step size.Automated Tracking Scheme Selection provides a mechanism to switch in an automated fashion between numerically stable lowerorder schemes and higher order schemes, which are stable only in a limited range. In situations where the particle is farfrom hydrodynamic equilibrium, an accurate solution can be achieved very quickly with a higher order scheme, since theseschemes need less step refinements for a certain tolerance. When the particle reaches hydrodynamic equilibrium, the higherorder schemes become inefficient since their step length is limited to a stable range. In this case, the mechanism switchesto a stable lower order scheme and facilitates larger integration steps.Including a Coupled Heat-Mass Solution on the Particles：This increased accuracy, however, comes at the expense of increasedcomputational expense.非稳态跟踪1）连续相稳态离散相非稳态：you simply enter the Particle Time Step Size and the Number of Time Steps, thus tracking particlesevery time a DPM iteration is conducted. When you increase the Number of Time Steps, the droplets penetrate the domain faster.2）连续离散相都为非稳态：When solving unsteady equations for the continuous phase, you must decide whether you want to UseFluid Flow Time Step to inject the particles, or whether you prefer a Particle Time Step Size independent of the fluid flowtime step. With the latter option, you can use the Discrete Phase Model in combination with changes in the time step forthe continuous equations, as it is done when using adaptive flow time stepping.随机轨道模型的参数：number of tries:An input of zero tells FLUENT to compute the particle trajectory based on the mean continuous phase velocityfield (Equation 23.2-1), ignoring the effects of turbulence on the particle trajectories. An input of 1 or greater tellsFLUENT to include turbulent velocity fluctuations in the particle force balance as in Equation 23.2-20.If you want the characteristic lifetime of the eddy to be random (Equation 23.2-32), enable the Random Eddy Lifetime option.You will generally not need to change the Time Scale Constant (CL in Equation 23.2-23) from its default value of 0.15,unless you are using the Reynolds Stress turbulence model (RSM), in which case a value of 0.3 is recommended.液滴颗粒碰撞与破碎碰撞：破碎：有两种模型，TAB 模型适合低韦伯数射流雾化以及低速射流进入标态空气中的情况。

资料范本本资料为word版本，可以直接编辑和打印，感谢您的下载第20章通用多相流模型--60页多相流数据后处理地点：__________________时间：__________________说明：本资料适用于约定双方经过谈判，协商而共同承认，共同遵守的责任与义务，仅供参考，文档可直接下载或修改，不需要的部分可直接删除，使用时请详细阅读内容20.通用多相流模型（General MultiphaseModels）本章讨论了在FLUENT中可用的通用的多相流模型。

第18章提供了多相流模型的简要介绍。

第19章讨论了Lagrangian离散相模型，第21章讲述了FLUENT中的凝固和熔化模型。

20.1选择通用多相流模型（Choosing a General Multiphase Model）20.2VOF模型(Volume of Fluid(VOF)Model)20.3混合模型(Mixture Model)20.4欧拉模型(Eulerian Model)20.5气穴影响(Cavity Effects)20.6设置通用多相流问题(Setting Up a General Multiphase Problem)20.7通用多相流问题求解策略(Solution Strategies for General Multiphase Problems)20.8通用多相流问题后处理(Postprocessing for General Multiphase Problems)20.1选择通用的多相流模型（Choosing a General Multiphase Model）正如在Section 18.4中讨论过的，VOF模型适合于分层的或自由表面流，而mixture和Eulerian模型适合于流动中有相混合或分离，或者分散相的volume fraction超过10%的情形。

（流动中分散相的volume fraction小于或等于10%时可使用第19章讨论过的离散相模型）。

20. 多相模型概述本章讨论了一般的多相模型。

20.1选择多相模型VOF模型适合于气液分层流动或者具有自有表面的流动，而混合模型和欧拉模型适合于相混合或者分开的流动或者分散相的体积分率大于10％的流动。

从欧拉模型和混合模型种选择，你需要考虑一下几点:1)如果分散相的的分布广，那么用混合模型最为合适。

如果分散相几种在主域的某些区域，那么用欧拉模型合适2)如果相间的drag law可用或者可以通过用户定义的方式得到，那么欧拉模型能得到精确的结果，如果相间的drag law不可知或者能否应用到你的问题中还是未知的情况下，选择混合模型。

20.1.1 VOFVOF模型能够通过求解一系列的动量方程并且跟踪主域中每种流体的体积分数来模拟两种或者两种以上不相混流体。

典型的应用有：jet breakup，液体中大气泡的运动，坝决口后水的运动，任何气液交界面的瞬态或稳态跟随。

VOF的不足：只能使用segregated solver；所有的控制体积必须要么充满单个流体相，要么充满混合相，不允许出现没有任何流体的区域。

只允许一个相可压缩Streamwise periodic flow not useSpecies mixing and reacting flow cannot be modeled不能用大涡湍流模型The second-order implicit time-stepping formulation cannot be used不能用于无粘流The shell conduction model for walls cannot be used稳态和瞬态求解：VOF方程的求解一般都是非定常的，但是对于某些问题，你只关心稳态解，那么你可以进行稳态求解。

A steady-state VOF calculation is sensible only when your solution is independent of the initial conditions and there are distinct inflow boundaries for the individual phases。