如何在fluent中设置多相流

3 设置一般的多相流问题 设置一般的多相流问题 Setting Up a General Multiphase Problem 3 1 使用一般多相流模型的步骤 使用一般多相流模型的步骤 Steps for Using the General Multiphase Models 设置和求解一般多相流问题的步骤的要点如下 各个子部分详细的讲述在随后的章节中 记住这里给出的仅是与 一般多相流计算相关的步骤 有关你使用的其它模型和相关的多相流模型的输入的详细信息 将在这些模型中合 适的部分给出 1 选中你想要使用的多相流模型 VOF mixture or Eulerian 并指定相数 Define Models Multiphase 2 从材料库中复制描述每相的材料 Define Materials 如果你使用的材料在库中没有 应创建一种新材料 如果你的模型中含有微粒 granular 相 你必须在 fluid materials category 中为它创建新材料 not the solid materials category 3 定义相 指定相间的相互作用 interaction 例如 使用欧拉模型时的 drag functions Define Phases 4 仅对欧拉模型 如果流动是紊流 定义多相紊流模型 Define Models Viscous 5 如果体积力存在 turn on gravity and specify the gravitational acceleration Define Operating Conditions 6 指定边界条件 包括第二相体积份额在流动边界和壁面上的接触角包括第二相体积份额在流动边界和壁面上的接触角 Define Boundary Conditions 7 设置模拟具体的解参数 Solve Controls Solution 8 初始化解和为第二相设定初始体积份额 为第二相设定初始体积份额 Solve Initialize Patch 9 计算求解和检查结果 欧拉多相流模拟的附加指南 欧拉多相流模拟的附加指南 Additional Guidelines for Eulerian Multiphase Simulations 一旦你决定了欧拉多相流模型适合你的问题 你应当考虑求解你的多相流问题的需求计算能力 要求的计算能 力很强的依赖于所求解的输运方程的个数和耦合程度 对欧拉多相流模型 有大数量的高度耦合的输运方程 计 算的耗费将很高 在设置你的问题前 尽可能减少问题的 statement 到最简化的可能形式 在你开始第一次求解尝试 取而代之尽力去求解多相流动的所有的复杂方面 你可以以简单近似地开始并且知 道问题定义的最终形式 简化多相流问题的一些建议列举如下 1 使用六面体或四边形网格 而不用四面体或三角形网格 2 减少相的数目 你会发现即使简单的近似也会给你的问题提供有用的信息 3 2 选用多相流模型并指定相数 选用多相流模型并指定相数 Enabling the Multiphase Model and Specifying the Number of Phases 为了选 VOF mixture Eulerian 多相流模型 在 Multiphase Model panel 下选 Volume of Fluid Mixture or Eulerian as the Model Define Models Multiphase 如果你选的欧拉模型 输入如下 number of phases 为了给多相流计算指定相数 在 Number of Phases 下下输入合适的值 你最多可以指定 20 相 optional cavitation effects 包含气穴影响 包含气穴影响 Including Cavitation Effects 对混合的欧拉模型计算 包含气穴影响是可能的 为了选气穴模型 在 Multiphase Model panel 中 Interphase Mass Transfer 下打开 Cavitation 由于气穴影响 接下来你应指定在使用传质计算时的两个参数 这些参数的指定应当于调查下的流动特征参 数相一致 Reynolds number and cavitation number 在 Multiphase Model panel 中 Cavitation Parameters 下面 2 设置 Vaporization Pressure PV 和 Bubble Number Density 的默认值是 10000 由 Kubota et al 推荐 默认的 PV值是 2367 8 环境温度下水的汽化压力 3 3 定义相概述 定义相概述 Overview of Defining the Phases 为了定义相 包括它们的材料属性 和相间的相互作用 例如 欧拉模型中的曳力函数 你将使用 Phases panel Figure 1 Define Phases Figure 1 The Phases Panel 这个面板中 Phase 下的每一项两类之一 如在 Type 列表中所示 primary phase 指出了所选项是主相 secondary phase 指出所选项是第二相 指定相之间的相互作用 点击 Interaction button 3 3 1 Defining the Primary Phase 定义主相定义主相 通常 你可以你喜欢的任何方式指定主相和第二相 考虑你的选择如何影响问题的设置是一种很好的主意 特别是在复杂的问题中 例如 对区域一部分中的一相 如果你计划 patch 其初始体积份额为 1 指定这个相为第 二相更方便 同样 如果一相是可压缩的 为了提高解的稳定性 建议你指定它为主相 记住 只能有一相是可压缩的 确定你没有选择可压缩材料 也就是对密度使用可压缩理想气体定律的材料 为多于一相的 1 Select phase 1 in the Phase list 2 Click Set and the Primary Phase panel Figure 2 will open Figure 2 The Primary Phase Panel 3 In the Primary Phase panel enter a Name for the phase 4 Specify which material the phase contains by choosing the appropriate material in the Phase Material drop down list 5 Define the material properties for the Phase Material Click Edit and the Material panel will open In the Material panel check the properties and modify them if necessary 3 If you make changes to the properties remember to click Change before closing the Material panel 6 Click OK in the Primary Phase panel 3 3 2 Defining a Non Granular Secondary Phase 定义非颗粒 即液体或气体 第二相定义非颗粒 即液体或气体 第二相 1 Select the phase e g phase 2 in the Phase list 2 Click Set and the Secondary Phase panel Figure 3 will open Figure 3 The Secondary Phase Panel for a Non Granular Phase 3 In the Secondary Phase panel enter a Name for the phase 4 Specify which material the phase contains by choosing the appropriate material in the Phase Material drop down list 5 Define the material properties for the Phase Material following the same procedure you used to set the material properties for the primary phase 6 In the Secondary Phase panel specify the Diameter of the bubbles or droplets of this phase You can specify a constant value or use a user defined function See the separate UDF Manual for details about user defined functions 7 Click OK in the Secondary Phase panel 3 3 3 Defining a Granular Secondary Phase 定义颗粒第二相定义颗粒第二相 1 Select the phase e g phase 2 in the Phase list 2 Click Set and the Secondary Phase panel Figure 4 will open 3 In the Secondary Phase panel enter a Name for the phase 4 Specify which material the phase contains by choosing the appropriate material in the Phase Material drop down list 5 Define the material properties for the Phase Material following the same procedure you used to set the material properties for the primary phase For a granular phase which must be placed in the fluid materials category You need to specify only the density you can ignore the values for the other properties since they will not be used In the Secondary Phase panel 6 Enable the Granular option 7 optional Enable the Packed Bed option if you want to freeze the velocity field for the granular phase Note that when you select the packed bed option for a phase you should also use the fixed velocity option with a 4 value of zero for all velocity components for all interior cell zones for that phase 8 Specify the Granular Temperature Model Choose either the default Phase Property option or the Partial Differential Equation option Figure 4 The Secondary Phase Panel for a Granular Phase 9 In the Secondary Phase dialog box specify the following properties of the particles of this phase Diameter specifies the diameter of the particles You can select constant in the drop down list and specify a constant value or select user defined to use a user defined function Granular Viscosity specifies the kinetic part of the granular viscosity of the particles s kin You can select constant the default in the drop down list and specify a constant value select syamlal obrien to compute the value select gidaspow to compute the value or select user defined to use a user defined function Granular Bulk Viscosity specifies the solids bulk viscosity q You can select constant the default in the drop down list and specify a constant value select lun et al to compute the value or select user defined to use a user defined function Frictional Viscosity specifies a shear viscosity based on the viscous plastic flow s fr By default the frictional viscosity is neglected as indicated by the default selection of none in the drop down list If you want to include the frictional viscosity you can select constant and specify a constant value select schaeffer to compute the value select johnson et al to compute the value or select user defined to use a user defined function Angle of Internal Friction specifies a constant value for the angle used in Schaeffer s expression for frictional viscosity This parameter is relevant only if you have selected schaeffer or user defined for the Frictional Viscosity 5 Frictional Pressure specifies the pressure gradient term Pfriction in the granular phase momentum equation Choose none to exclude frictional pressure from your calculation johnson et al syamlal obrien based ktgf where the frictional pressure is defined by the kinetic theory The solids pressure tends to a large value near the packing limit depending on the model selected for the radial distribution function You must hook a user defined function when selecting the user defined option Frictional Modulus is defined as with G 0 which is the derived option You can also specify a user defined function for the frictional modulus Friction Packing Limit specifies a threshold volume fraction 开始体积分数 at which the frictional regime becomes dominant It is assumed that for a maximum packing limit of 0 6 the frictional regime starts at a volume fraction of about 0 5 This is only a general rule of thumb as there may be other factors involved Granular Conductivity specifies the solids granular conductivity k s You can select syamlal obrien to compute the value select gidaspow to compute the value or select user defined to use a user defined function Note however that ANSYS FLUENT currently uses an algebraic relation for the granular temperature This has been obtained by neglecting convection and diffusion in the transport equation Granular Temperature specifies temperature for the solids phase and is proportional to the kinetic energy of the random motion of the particles Choose either the algebraic the constant or user defined option Solids Pressure specifies the pressure gradient term Ps in the granular phase momentum equation Choose either the lun et al the syamlal obrien the ma ahmadi none or a user defined option Radial Distribution specifies a correction factor that modifies the probability of collisions between grains when the solid granular phase becomes dense Choose either the lun et al the syamlal obrien the ma ahmadi the arastoopour or a user defined option Elasticity Modulus is defined as with Packing Limit specifies the maximum volume fraction for the granular phase s max For mono dispersed spheres the packing limit is about 0 63 which is the default value in ANSYS FLUENT In poly dispersed cases however smaller spheres can fill the small gaps between larger spheres so you may need to increase the maximum packing limit 10 Click OK in the Secondary Phase dialog box 6 3 3 4 Defining the Interfacial Area Concentration To define the interfacial area concentration on the secondary phase in the Eulerian model perform the following steps 1 Select the phase e g phase 2 in the Phases list 2 Click Edit to open the Secondary Phase dialog box 3 In the Secondary Phase dialog box enter a Name for the phase 4 Specify which material the phase contains by choosing the appropriate material in the Phase Material drop down list 5 Define the material properties for the Phase Material 6 Enable the Interfacial Area Concentration option Make sure the Granular option is disabled for the Interfacial Area Concentration option to be visible in the interface 7 In the Secondary Phase dialog box specify the following properties of the particles of this phase Diameter specifies the diameter of the particles or bubbles You can select constant in the drop down list and specify a constant value or select user definedto use a user defined function See the separate UDF Manual for details about user defined functions The Diameter recommended setting is sauter mean allowing for the effects of the interfacial area concentration values to be considered for mass momentum and heat transfer across the interface between phases Packing Limit specifies the maximum volume fraction for the particle bubble phase Growth Rate allows you to specify the particle growth rate m s You can select none constant or user defined from the drop down list If you selectconstant specify a value in the adjacent field If you have a user defined function UDF that you want to use to model the growth rate you can choose the user defined option and specify the appropriate UDF Coalescence Kernal and Breakage Kernel allows you to specify the coalescence and breakage kernels You can select none constant hibiki ishii ishii kim or user defined In addition to specifying the hibiki ishii and ishii kim as the coalescence and breakage kernels you can also tune the properties of these two models by using the define phases iac expert hibiki ishii model and define phases iac expert ishii kim model text commands For the Hibiki Ishii model you can specify the following parameters Coefficient Gamma c Coefficient K c Coefficient Gamma b Coefficient K b alpha max For the Ishii Kim model you can specify the following parameters Coefficient Crc Coefficient Cwe Coefficient C Coefficient Cti alpha max 3 3 5 Defining the Interaction Between Phases 对颗粒和非颗粒流动 你必须指定在动量交换系数的计算中使用的曳力函数 对颗粒流 你也必须指定颗粒 碰撞的归还系数 归还系数 restitution coefficients 为颗粒和非颗粒流动包含可选的升力和虚拟质量力升力和虚拟质量力 下面描述 也是 可能的 为指定这些参数 click Interaction to open the Phase Interaction panel Figure 5 1 Specifying the Drag Function FLUENT 允许你为一对相指定曳力函数 步骤如下 a Click the Drag tab to display the Drag Function inputs b 对每一对相 从下面相应的列表中选择合适的曳力函数 1 Select schiller naumann to use the fluid fluid drag function The Schiller and Naumann model is the default method and it is acceptable for general use in all fluid fluid multiphase calculations 2 Select morsi alexander to use the fluid fluid drag function The Morsi and Alexander model is the most complete adjusting the function definition frequently over a large range of Reynolds numbers but calculations with this model may be less stable than with the other models 3 Select symmetric to use the fluid fluid drag function described The symmetric model is recommended for 7 flows in which the secondary dispersed phase in one region of the domain becomes the primary continuous phase in another For example if air is injected into the bottom of a container filled halfway with water the air is the dispersed phase in the bottom half of the container in the top half of the container the air is the continuous phase 4 Select wen yu to use the fluid solid drag function The Wen and Yu model is applicable for dilute phase flows in which the total secondary phase volume fraction is significantly lower than that of the primary phase 5 Select gidaspow to use the fluid solid drag function The Gidaspow model is recommended for dense fluidized beds 6 Select syamlal obrien to use the fluid solid drag function The Syamlal O Brien model is recommended for use in conjunction with the Syamlal O Brien model for granular viscosity 7 Select syamlal obrien symmetric to use the solid solid drag function The symmetric Syamlal O Brien model is appropriate for a pair of solid phases 8 Select constant to specify a constant value for the drag function and then specify the value in the text field 9 Select user defined to use a user defined function for the drag function see the separate UDF Manual for details 10 If you want to temporarily ignore the interaction between two phases select none Figure 5 The Phase Interaction Panel for the Eulerian Model 2 Specifying the Restitution Coefficients Granular Flow Only 对颗粒流 你必须为颗粒间的碰撞指定归还系数 eIs and ess 除了为每一对颗粒相之间的碰撞指定归还系数 外 你也得为同相颗粒之间的碰撞指定归还系数 步骤如下 Click the Collisions tab to display the Restitution Coefficient inputs For each pair of phases specify a constant restitution coefficient All restitution coefficients are equal to 0 9 by default 3 Including the Lift Force 对颗粒和非颗粒流 在第二相颗粒 液滴 或气泡中包含升力 Flift 的影响是可能的 这些升力作用于颗粒 液滴或气泡主要是由于主相流场中的速度梯度 在大多数情形下 升力与曳力相比是不重要的 因此没必要包含 8 它 如果升力重要 也就是说 如果相很快分离 你可以包含这个影响 注意注意对大颗粒 升力更重要 但是 FLUENT 模型假设粒子直径远小于粒子间距离 这样对接近充满的颗粒 closely packed particles 或者小颗粒 包含升力是不合适的 包含升力影响的步骤如下 a Click the Lift tab to display the Lift Coefficient inputs b 对每一对相 从下面相应的列表中选择合适的指定方法 注意 既然作用于颗粒 液滴或气泡的升力主要是由 于主相流场中的速度梯度 你不必为存在于两个第二相间的每对相指定升力系数 只对存在于第二相和主相之 间的每对相指定升力系数 Select none the default to ignore the effect of lift forces Select constant to specify a constant lift coefficient and then specify the value in the text field Select user defined to use a user defined function for the lift coefficient see the separate UDF Manual for details 4 Including the Virtual Mass Force 对颗粒和非颗粒流 当第二相相对于主相加速时包含存在的虚拟质量力 Fvm 是可能的 当第二相的密度远 小于主相的密度时虚拟质量的影响是重要的 也就是对瞬态泡状柱流 transient bubble column 包含虚拟质量力的影响 turn on the Virtual Mass option in the Phase Interaction panel 虚拟质量力的影响被包含在所有第二相内 使它仅为颗粒相是不可能的 5 Including Body Force 包含体积力包含体积力 在许多情况下 相的运动部分是由于重力的影响 为了包含这个体积力 应在 Operating Conditions panel 下选 择 Gravity 并且指定 Gravitational Acceleration Define Operating Conditions 对于 VOF 计算 你应当在 Operating Conditions panel 下选择 Specified Operating Density 并且在 Operating Density 下为最轻相设置密度 这种排除了水力静压的积累 提高了 round off 精度为动量平衡 如果任何一 相都是可压缩的 设置 Operating Density 为零 对于涉及体积力的 VOF 和 mixture 计算 建议你在 Multiphase Model panel 下为 Body Force Formulation 选择 Implicit Body Force 这种处理通过解决压力梯度和动量方程中体积力的部分平衡提高了解的收敛 3 4 为为 Eulerian 多相流计算选择紊流模型多相流计算选择紊流模型 如果你使用 Eulerian 模型求解紊流 你必须在三种紊流模型中选择一种模型 在 Viscous Model panel Figure 6 步骤如下 1 Select k epsilon under Model 2 Select the desired k epsilon Model and any other related parameters as described for single phase calculations 3 Under k epsilon Multiphase Model indicate the desired multiphase turbulence model Select Mixture to use the mixture turbulence model This is the default model Select Dispersed to use the dispersed turbulence model This model is applicable when there is clearly one primary continuous phase and the rest are dispersed dilute secondary phases Select Per Phase to use a k turbulence model for each phase This model is appropriate when the turbulence transfer among the phases plays a dominant role 包含源项 包含源项 Including Source Terms 默认情形 相间动量 源项不包含在计算中 如果你想包含这些源项中的任一项 你可以使用 multiphase options command in the define models viscous multiphase turbulence text menu 注意 包含这些项明显减 慢收敛速度 如果你要寻找额外的精度 你应首先求的没有这些源项的解 接着包含上这些源项计算 大多数 情形下这些源项可以忽略 9 Figure 6 The Viscous Model Panel for an Eulerian Multiphase Calculation 3 5 设置边界条件设置边界条件 多相流边界条件的设置在 Boundary Conditions panel Figure 7 中进行 但是设置多相流边界条件的步骤与单 相流模型有些不同 你必须分别为各个相设置一些条件 而其他的条件是所有相 也就是 mixture 所共享的 如 下有详细的描述 3 5 1Define Boundary Conditions 混合相 混合相 mixture 和各个单相的边界条件 和各个单相的边界条件 Figure 7 The Boundary Conditions Panel 如果你使用的是 Eulerian 模型 你必须为每一个区域类型指定的条件列举如下并总结在表 1 2 3 和 4 注 具 10 体的紊流参数取决于你使用的三个多相紊流模型 说明在表 2 4 中 对于 exhaust fan outlet vent or pressure outlet 如果你使用层流模型或使用混合紊流模型 默认的多相 紊流模型 没有条件为主相设置 对于每个第二相 你必须设置 volume fraction 为常数 型线或者 UDF 如果相是颗粒的 granular 你也 必须设置颗粒温度 granular tempreture 如果你使用的混合紊流模型 你必须为 mixture 指定紊流边界条件 如果你使用的是分散 dispersed 紊流模型 你必须为主相设置它们 如果你使用的是 per phase 紊流模型 你必须为主相和第二相设置 它们 所有其他条件都是为 mixture 设置的 对于 velocity inlet 你必须为每一相指定速度 对于第二相 你必须设置 volume fraction 如上所述 如果相是颗粒的 granular 你也必须设置颗粒 温度 granular temperature 如果你使用的是 mixture 紊流模型 你必须为 mixture 设置紊流边界条件 如果你使用的是分散 dispersed 紊流模型 你必须为主相指定它们 如果你使用的是 per phase 紊流模型 你必须为主相 和第二相设置它们 所有其他的条件都是为 mixture 设置的 对于 axis outflow periodic solid or symmetry zone 所有条件都是为 mixture 设置的 没有条件为单相 设置 对于 wall zone shear 条件为单相指定 所有其他条件为 mixture 指定 对于 fluid zone 所有 source terms 和 fixed values 都是为单相设置的 除非你使用的是 mixture 紊流模型 或 dispersed 紊流模型 如果你使用的是 mixture 紊流模型 紊流的 source terms 和 fixed values 为 mixture 设置 如果你使用的是 dispersed 紊流模型 他们只为主相设置 如果 fluid zone 不是多孔的 所有其他条件都是为 mixture 设置 如果 fluid zone 是多孔的 你将为混合相混合相选择 Porous Zone 在 Fluid 面板下 Porosity input