1、3 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（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
2、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 an
3、d 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。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。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（Additional Guidelines for Eulerian Multiphase Simulations）一旦你决定了
4、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（Enabli
5、ng 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 下输入合适的值。你最多可以指定 20 相。 (optional) cavit
6、ation effects：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 Vaporiz
7、ation 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（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：pri
8、mary-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！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
9、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 Panel3) 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 Pha
10、se 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 Materia
11、l 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 Phase3) In the S
12、econdary 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 t
13、he 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 Defin
14、ing a Granular Secondary Phase 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
15、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 densit
16、y; 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
17、 for a phase, you should also use the fixed velocity option with a 4value 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: T
18、he Secondary Phase Panel for a Granular Phase9) 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
19、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
20、, 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 fun
21、ction. 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 spec
22、ify 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 Schaeffers expression for frictional viscosity. This parameter i
23、s relevant only if you have selected schaeffer or user-defined for the Frictional Viscosity.5 Frictional Pressure specifies the pressure gradient term, P friction, in the granular-phase momentum equation. Choose none to exclude frictional pressure from your calculation, johnson-et-al, syamlal-obrien
24、, 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. Friction
25、al Modulus is defined as with G0, 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
26、 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 (ks ). You can select syamlal-obrien to compute the value, select gidaspow to compute
27、 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
28、 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, t
29、he 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,
30、 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 s
31、pheres 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.63.3.4 Defining the Interfacial Area ConcentrationTo define the interfacial area concentration on the secondary phase in the Eulerian model, per
32、form 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 Materi
33、al 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 fol
34、lowing 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
35、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 pha
36、se. 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
37、 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
38、 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, Coe
39、fficient K_c, Coefficient Gamma_b, Coefficient K_b, alpha_maxFor the Ishii-Kim model, you can specify the following parameters: Coefficient Crc, Coefficient Cwe, Coefficient C, Coefficient Cti, alpha_max3.3.5 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
40、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（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 FunctionFLUENT 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-
41、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, adj
42、usting 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 7flows in which the secondary (
43、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 t
44、he 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. Th
45、e Gidaspow model is recommended for dense fluidized beds.（6） Select syamlal-obrien to use the fluid-solid drag function. The Syamlal-OBrien model is recommended for use in conjunction with the Syamlal-OBrien model for granular viscosity.（7） Select syamlal-obrien-symmetric to use the solid-solid drag
46、 function. The symmetric Syamlal-OBrien 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 U
47、DF 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 Model2) 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（e Is 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
48、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（F lift）的影响是可能的。这些升力作用于颗粒、液滴或
49、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 constan
