多相流模型经验谈

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 the Euler-Euler approach.

The Euler-Lagrange Approach:The Lagrangian discrete phase model in FLUENT follows the Euler-Lagrange approach, this approach

is inappropriate for the modeling of liquid-liquid mixtures, fluidized beds, or any application where the volume fraction

of 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 is

of interest. Applications of the VOF model include stratified flows, free-surface flows, filling, sloshing, the motion of

large bubbles in a liquid, the motion of liquid after a dam break, the prediction of jet breakup (surface tension), and the

steady 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 model homogeneous 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 Phase

Iterations 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 particle

source terms are recalculated.

Length Scale: controls the integration time step size used to integrate the equations of motion for the particle.A smaller

value for the Length Scale increases the accuracy of the trajectory and heat/mass transfer calculations for the discrete phase.

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 relaxation times.

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 an

automated 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 exceeded

the 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 lower

order schemes and higher order schemes, which are stable only in a limited range. In situations where the particle is far

from hydrodynamic equilibrium, an accurate solution can be achieved very quickly with a higher order scheme, since these

schemes need less step refinements for a certain tolerance. When the particle reaches hydrodynamic equilibrium, the higher

order schemes become inefficient since their step length is limited to a stable range. In this case, the mechanism switches

to 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 increased computational 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 particles

every 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 Use

Fluid Flow Time Step to inject the particles, or whether you prefer a Particle Time Step Size independent of the fluid flow

time step. With the latter option, you can use the Discrete Phase Model in combination with changes in the time step for

the 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 velocity

field (Equation 23.2-1), ignoring the effects of turbulence on the particle trajectories. An input of 1 or greater tells

FLUENT 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。对韦伯数大于100 的情况，波动模型适应性较好。 在高速燃料射流雾化中，波动模型应用甚广。

对于TAB 模型，用户需要在y0 文本框中设定y0的值。The default value (y0 = 0) is recommended.

对于Y波动模型，需要输入B0与B1，you will generally not need to modify the value of B0, as the default value 0.61 is acceptable

for nearly all cases. A value of 1.73 is recommended for B1.

颗粒类型中的燃烧类型

燃烧（``combusting''）颗粒是一种固体颗粒，它遵从由方程19.2-1 所确定的受力平衡、由定律1 所确定的加热冷却过程、由定律4 所确定

的挥发份析出过程（19.3.5 节）以及由定律5 所确定的异相表面反应机制（19.3.6 节）。最后，当颗粒的挥发份完全析出之后，非挥发份 的运动、变化由定律6 所确定。在Set Injection Properties panel 面板中选定Wet Combustion 选项，用户可以在燃烧颗粒中包含有可蒸发

物质。这样，颗粒的可蒸发物质可在挥发份开始析出之前，经历由定律2、3 所确定的蒸发与沸腾过程.

若定义的是Combusting 燃烧类型颗粒，可在Devolatilizing Species 下拉列表框下选定由挥发份析出定律4 确定的气相组分，参与焦炭表面

燃烧反应（定律5）的气相组分列于Oxidizing Species（氧化剂组分）列表中，有表面反应生成的气相组分则列于ProductSpecies（生成物组

分）列表中。需要注意的是，对于选定的燃烧颗粒介质，如果燃烧模型为multiple-surface -reaction 多表面异相反应模型，那么，由于化学 反应计量比在混合介质中已经被确定，所以Oxidizing Species 与Product Species 列表将变灰（不可选）。

液滴喷射类型

平面雾化模型的输入

l 位置：在X-, Y-, and Z-Position 文本框区可以设定射流的沿直角坐标的三向位置（在三维情况下才会有Z-Position 出现）

l 速度：在X-, Y-, and Z- Velocity 文本框区可以设定射流初始速度沿直角坐标的三向分量 （在三维情况下才会有Z- Velocity 出现） l 轴的方向（仅适用于三维）：设定确定喷嘴轴线方向的三个分量，在X-Axis, Y-Axis, and Z-Axis 区设定。

l 温度：在Temperature 区可设定喷射颗粒流的初始颗粒（绝对）温度。 l 质量流率：可在Flow Rate 区设定喷嘴的的颗粒质量流量。 l 射流持续时间：对于非稳态颗粒跟踪计算（请参阅19.8 节），在Start Time 和Stop Time 区设定喷射的开始于结束时间。

l 蒸气压：设定控制通过喷嘴内部流动的蒸气压（表19.4.1 中的pv ），在Vapor Pressure 区设定。

l 直径：设定喷嘴直径（表19.4.1 中的d ），在Injector Inner Diam.区设定。 l 喷嘴长度：设定喷嘴的长度（表19.4.1 中的L ），在Orifice Length 区设定。 l 内台阶角半径（导角半径）：设定喷嘴内台阶处的导角半径（表19.4.1 中的r ），在Corner Radius of Curv.区设定。

l 喷嘴参数：设定射流角修正系数（方程19.4-16 中的 CA ），在Constant A 区设定。{CA=3+L/3.6/d,喷射角度的大小强烈依赖于喷嘴的

内部流动。因此，对于空穴喷嘴，用户设定的CA 值应该比单相流的要小才可以。CA 的常见取值范围为4.0～6.0。返流喷嘴的喷射角度更小 }

l 方位角：设定三维情况下的喷嘴方位开始角与结束角，在Azimuthal Start Angle and

Azimuthal Stop Angle 区设定。

压力－旋流雾化喷嘴的点属性设定(气体透平工业的人把它称作单相喷嘴（simplex atomizer）。这种喷嘴，然后流体通过一个称作旋流片

的喷头被加速后，进入中心旋流室。在旋流室内，旋转的液体被挤压到固壁，在流体中心形成空气柱，然后，液体以不稳定的薄膜状态从 喷口喷出，破碎成丝状物及液滴。)

l 射流角：在Spray Half Angle 区下设定射流喷射半角（方程19.4-25 中的θ ）。 l 压力：在Upstream Pressure 区下设定喷嘴上游压力（表19.4.1 中的p1 ）。

l 液膜破碎常数：设定确定液膜破碎时形成的线状液膜长度的一个经验常数（方程19.4-30中的ln（ηb/η0），在Sheet Constant 设定。 {ln（ηb/η0）为3～12 的经验常数。这个值必须由用户设定，其缺省值为12 with experimental sheet breakup lengths over a range of Weber numbers from 2 to 200.}

l 线状液膜直径：对于短波，确定液膜破碎波长与线状液膜半径之间的线形比例关系的比例常数，在Ligament Constant 区设定。

{where CL, or the ligament constant, is equal to 0.5 by default.}

空气辅助雾化喷嘴的点属性设定(为了加速液膜的破碎，喷嘴经常会添加上辅助空气。液体通过喷座的作用形成液膜,空气则直接冲击液膜 以加速液膜的破碎。)

l 喷嘴外半径：在Injector Outer Diam. 区下设定射流的外部半径。此数值与喷嘴内部半径共同确定了液膜厚度（方程19.4-22 中的t ）。 l 射流角：设定射流离开喷口时的液膜初始轨道（方程19.4-25 中的θ ），在Spray Half Angle 区设定。

l 相对速度：设定液膜与空气之间的最大相对速度，在Relative Velocity 区设定。

l 液膜破碎常数：设定确定液膜破碎时形成的线状液膜长度的一个经验常数（方程19.4-30中的ln（ηb/η0）），在Sheet Constant 区设定。

l 线状液膜直径：对于短波，确定液膜破碎波长与线状液膜半径之间的线形比例关系的比例常数，在Ligament Constant 区设定。

{where CL, or the ligament constant, is equal to 0.5 by default.}

平板扇叶雾化喷嘴的点属性设定(液体从宽而薄的喷口出来后形成平面液膜，继而破碎成液滴。只有在三维的情况下才可以使用这个模型)

l 扇叶中心点：设定射流源起始位置的三向坐标值（请参阅图19.4.6），在X-Center,Y-Center, and Z-Center 区设定。

l 虚点位置：设定喷嘴扇叶的各边的虚拟交叉点（请参阅图19.4.6），在X-Virtual Origin, Y-Virtual Origin, and Z-Virtual Origin 区设定。

l 垂直方向：设定垂直扇叶的向量的各个分量，在X-Fan Normal Vector, Y-Fan Normal Vector, and Z-Fan Normal Vector 区设定。

l 温度：设定颗粒流的温度，在Temperature 区设定。

l 质量流量：设定喷嘴的质量流量，在Flow Rate 区设定。 l 射流持续时间：对于非稳态颗粒跟踪计算（请参阅19.8 节），在Start Time 和Stop Time 区设定喷射的开始于结束时间。

l 射流角：在Spray Half Angle 区下设定射流喷射半角。

l 喷口宽度：设定喷口垂直方向的宽度，在Orifice Width 区设定。

l 液膜破碎常数：设定确定液膜破碎时形成的线状液膜长度的一个经验常数（请参阅方程19.4-30的ln（ηb/η0）），在Flat Fan Sheet Constant 区设定。

气泡雾化喷嘴的点属性设定(，液体中混合了过热液体或者类似的介质。当挥发性液体从喷口喷出时，迅速发生相变。相变使流体迅速以很大

的分散角破碎成小液滴。此模型也适用于热流体射流。) 混合情况参数：设定射流中液－气混合物中已蒸发的液滴质量分数（方程19.4-38 中的x ），在Mixture Quality 区设定。

l 饱和温度：设定可挥发成分的饱和温度，在Saturation Temp.区设定。

l 液滴扩散系数：设定控制液滴在空间扩散性能的扩散系数（方程19.4-38 中的 Ceff ），在Dispersion Constant 区设定。

l 射流角：设定液膜离开喷口时的初始轨道方向角，在Maximum Half Angle 区设定。

通用多相流模型

mixture model VS euler model

1)If there is a wide distribution of the dispersed phases (i.e., if the particles vary in size and the largest particles

do not separate from the primary flow field), the mixture model may be preferable (i.e., less computationally expensive). If the

dispersed phases are concentrated just in portions of the domain, you should use the Eulerian model instead.

If interphase drag laws that are applicable to your system are available (either within FLUENT or through a user-defined

function), the Eulerian model can usually provide more accurate results than the mixture model. Even though you can apply

the same drag laws to the mixture model, as you can for a non-granular Eulerian simulation, if the interphase drag laws are

unknown or their applicability to your system is questionable, the mixture model may be a better choice. For most cases

with spherical particles, then the Schiller-Naumann law is more than adequate. For cases with non-spherical particles, then

a user-defined function can be used.

加快收敛求解策略

You can increase the size of the time step after performing a few time steps. For steady solutions it is recommended that

you start with a small under-relaxation factor for the volume fraction, Another option is to start with a mixture multiphase

calculation, and then switch to the Eulerian multiphase model.

VOF模型

界面之间的scalar梯度不要太大

界面插值：there are four scheme for interface interpolation:geometric reconstruction, donor-acceceptor, euler explicit,

inexplicit,The geometric reconstruction scheme represents the interface between fluids using a piecewise-linear approach.

In FLUENT this scheme is the most accurate and is applicable for general unstructured meshes. the donor-acceptor scheme can

be used only with quadrilateral or hexahedral meshes.The implicit scheme can be used for both time-dependent and steady-state calculations.

Euler model中的附加作用力

Lift Forces:In most cases, the lift force is insignificant compared to the drag force, so there is no reason to include this extra term. If the lift force is significant (e.g., if the phases separate quickly), it may be appropriate to include this term.

The virtual mass effect is significant when the secondary phase density is much smaller than the primary phase density

(e.g., for a transient bubble column). By default, virtual mass effect is not included.

多相湍流模型 k-e model

k-e mixture model（default） it is applicable when phases separate, for stratified (or nearly stratified) multiphase flows,

and when the density ratio between phases is close to 1.，它应用于相分离，分层（或接近分层）的多相流，和相之间的密度比接近1。

The dispersed turbulence model is the appropriate model when the concentrations of the secondary phases are dilute. In this

case, interparticle collisions are negligible and the dominant process in the random motion of the secondary phases is the

influence of the primary-phase turbulence.当明显地有一个主连续相和其它的是分散稀释的第二相时，这个模型是适用的。The drift

velocity results from turbulent fluctuations in the volume fraction.This correction is not included, by default, but you

can enable it during the problem setup(define －－－model－－－multiphases-option).

k-e Turbulence Model for Each Phase:This turbulence model is the appropriate choice when the turbulence transfer among the phases plays a dominant role.

RSM model

Multiphase turbulence modeling typically involves two equation models that are based on single-phase models and often

cannot accurately capture the underlying flow physics.there are two options for Rsm model, mixture and dispersed turbulence model.

Wet Steam Model

通用多相流模型的输入：

1)vof model

number of phases:

VOF formulation: 1)Time-dependent with the geometric reconstruction interpolation scheme: This formulation should be used

whenever you are interested in the time-accurate transient behavior of the VOF solution. 2)Time-dependent with the

donor-acceptor interpolation scheme: This formulation should be used instead of the time-dependent formulation with the

geometric reconstruction scheme if your mesh contains highly twisted hexahedral cells. For such cases, the donor-acceptor

scheme may provide more accurate results. 3)Time-dependent with the Euler explicit interpolation scheme: Since the

donoracceptor scheme is available only for quadrilateral and hexahedral meshes, it cannot be used for a hybrid mesh

containing twisted hexahedral cells. For such cases, you should use the time-dependent Euler explicit scheme.While the

Euler explicit time-dependent formulation is less computationally expensive than the geometric reconstruction scheme, the

interface between phases will not be as sharp as that predicted with the geometric reconstruction scheme. To reduce this

diffusivity, it is recommended that you use the second-order discretization scheme for the volume fraction equations.

4)Time-dependent with the implicit interpolation scheme: This formulation can be used if you are

looking for a steady-state

solution and you are not interested in the intermediate transient flow behavior, but the final steady-state solution is

dependent on the initial flow conditions and/or you do not have a distinct inflow boundary for each phase. 5)Steady-state

with the implicit interpolation scheme: This formulation can be used if you are looking for a steady-state solution, you

are not interested in the intermediate transient flow behavior, and the final steady-state solution is not affected by the

initial flow conditions and there is a distinct inflow boundary for each phase. Note that the implicit modified HRIC scheme

can be used as a robust alternative to the explicit geometric reconstruction scheme.

Including Body Forces:In many cases, the motion of the phases is due, in part, to gravitational effects. To include this

body force, turn on Gravity in the Operating Conditions panel and specify the Gravitational Acceleration. For VOF

calculations, you should also turn on the Specified Operating Density option in the Operating Conditions panel, and set the

Operating Density to be the density of the lightest phase. If any of the phases is compressible, set the Operating Density to zero.

Modeling Open Channel Flows:FLUENT can model the effects of open channel flow (e.g., rivers, dams, and surfacepiercing

structures in unbounded stream) using the VOF formulation and the open channel boundary condition. the steps to open open

channel flows are:1. Turn on gravity 2. Enable the volume of fluid model and select Open Channel Flow.

boundary conditions setting for open channel flow: 1)Determining the Free Surface Level(ylocal) We can simply calculate

the free surface level in two steps: 1. Determine the absolute value of height from the free surface to the origin in the

direction of gravity. 2. Apply the correct sign based on whether the free surface level is above or below the origin. If

the liquid's free surface level lies above the origin, then the Free Surface Level is positive (see Figure 24.8.2). Likewise,

if the liquid's free surface level lies below the origin, then the Free Surface Level is negative. 2)Determining the Bottom

Level(ybottom): We can simply calculate the bottom level in two steps: 1. Determine the absolute value of depth from the

bottom level to the origin in the direction of gravity. 2. Apply the correct sign based on whether the bottom level is above

or below the origin. 3)Specifying the Total Height ytot = ylocal+V*V/2/g 4)Determining the

Velocity Magnitude(appear in

the pressure inlet) This is to be specified as the magnitude of the upstream inlet velocity in the flow 5)Determining

the Secondary Phase for the Inlet Consider a problem involving a three-phase flow consisting of air as the primary phase,

and oil and water as the secondary phases. Consider also that there are two inlet groups:1. water and air 2. oil and air;

For the first inlet group, you would choose water as the secondary phase. For the second inlet group, you would choose oil as the secondary phase.

liminations of channel flow:Limitations:The following list summarizes some issues and limitations associated with the open channel boundary condition.

1. The conservation of the Bernoulli integral does not provide the conservation of mass flow rate for the pressure boundary.

In the case of a coarser mesh, there can be a significant difference in mass flow rate from the actual mass flow rate. For

finer meshes, the mass flow rate comes closer to the actual value. So, for problems having constant mass flow rate, the mass flow rate boundary condition is a better option. The pressure boundary should be selected when steady and non-oscillating drag is the main objective.

2. Specifying the top boundary as the pressure outlet can sometimes lead to a divergent solution. This may be due to the

corner singularity at the pressure boundary in the air region or due to the inability to specify local flow direction

correctly if the air enters through the top locally.

3. Only the heavier phase should be selected as the secondary phase.

4. In the case of three-phase flows, only one secondary phase is allowed to enter through one inlet group. That means, the

mixed inflow of different secondary phases is not allowed.

Defining Phases for the VOF Model:1)In general, you can specify the primary and secondary phases whichever way you prefer.

It is a good idea, especially in more complicated problems, to consider how your choice will affect the ease of problem

setup. For example, if you are planning to patch an initial volume fraction of 1 for one phase in a portion of the domain,

it may be more convenient to make that phase a secondary phase. Also, if one of the phases is a compressible ideal gas, it

is recommended that you specify it as the primary phase to improve solution stability.

Including Surface Tension and Wall Adhesion Effects(Surface tension effects can be neglected if Ca》1 or We》1. For

calculations involving surface tension, it is recommended that you also turn on the Implicit Body

Force treatment for the

Body Force Formulation in the Multiphase Model panel. This treatment improves solution convergence by accounting for the

partial equilibrium of the pressure gradient and surface tension forces in the momentum equations) :you must specify surface tension coefficient.

you can considering wall adhesion by turning on wall adhesion in phases interaction panel. you must input the contact angle

in the wall boundary condition. The default value for all pairs is 90 degrees, which is equivalent to no wall adhesion

effects (i.e., the interface is normal to the adjacent wall). A contact angle of 45 degree, for example, corresponds to

water creeping up the side of a container, as is common with water in a glass.

time dependent solution

If you want FLUENT to solve the volume fraction equation(s) at every iteration within a time step, turn on the Solve VOF

Every Iteration option under VOF Parameters. This choice is the less stable of the two, and requires more computational

effort per time step than the default choice.

库兰数的设定：if the maximum allowed Courant number is 0.25 (the default), the time step will be chosen to be at most

one-fourth the minimum transit time for any cell near the interface.

2) mixture model的输入

number of phases: as above Including Body Forces: as above

whether or not to compute the slip velocities ：by default, fluent turn on the compute the slip velocities, if you are

Defining a Homogeneous Multiphase Flow, turn off the compute slip velocities.

Defining a Granular Secondary Phase:

Packing Limit specifies the maximum volume fraction for the granular phase . For monodispersed spheres, the packing limit

is about 0.63, which is the default value in FLUENT. In polydispersed cases, however, smaller spheres can fill the small

gaps between larger spheres, so you may need to increase the maximum packing limit.

Including Cavitation Effects:To enable the cavitation model, turn on the Cavitation option in the Mass tab of the Phase

Interaction panel. you must set the Vaporization Pressure , the Surface Tension Coefficient , and the mass fraction of Non

Condensable Gas. When multiple species are included in one or more secondary phases, or the heat transfer due to phase

change needs to be taken into account, the mass transfer mechanism must be defined before turning on the Cavitation option.

It may be noted, however, that for cavitation problems, at least two mass transfer mechanisms are defined:

1. Mass transfer from liquid to vapor. 2. Mass transfer from vapor to liquid.

3) euler model 输入

number of phases: as above Including Body Forces: as above

Defining a Granular Secondary Phase:

Granular Temperature

Algebraic formulation (the default). It is obtained by neglecting convection and diffusion in the transport equation, Equation 24.4-68 [340].

Partial Differential Equation. This is given by Equation 24.4-68 and it is allowed to choose different options for it properties.

Constant Granular Temperature. This is useful in very dense situations where the random fluctuations are small.

Packing Limit specifies the maximum volume fraction for the granular phase . For monodispersed spheres, the packing limit

is about 0.63, which is the default value in FLUENT. In polydispersed cases, however, smaller spheres can fill the small

gaps between larger spheres, so you may need to increase the maximum packing limit.

Defining the Interaction Between Phases

define the drag fuction:

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.

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.

Select symmetric to use the fluid-fluid drag function. The symmetric model is recommended for 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.

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. Select gidaspow to use the fluid-solid drag function. The Gidaspow model is recommended for dense fluidized beds.

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.

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.

Select constant to specify a constant value for the drag function, and then specify the value in the text field.

Select user-defined to use a user-defined function for the drag function.

If you want to temporarily ignore the interaction between two phases, select none.

Specifying the Restitution Coefficients (Granular Flow Only):For granular flows, you need to specify the coefficients of

restitution for collisions between particles All restitution coefficients are equal to 0.9 by default

Including the Lift Force(Note that the lift force will be more significant for larger particles, but the FLUENT model

assumes that the particle diameter is much smaller than the interparticle spacing. Thus, the inclusion of lift forces is

not ppropriate for closely packed particles or for very small particles.)

Including the Virtual Mass Force(The virtual mass effect is significant when the secondary phase density is much smaller

than the primary phase density) turn on the virtual mass in the phase interaction panel to include the virtual mass force effect.

Defining Heat Transfer between the two phases for the Eulerian Model:1)gunn is frequently used for Eulerian multiphase

simulations involving a granular phase. 2)ranz-marshall is frequently used for Eulerian multiphase

simulations not

involving a granular phase.

3)none allows you to ignore the effects of heat transfer between the two phases

the turbulence in euler model

湍流模型中包含包含源项（Including Source terms）:默认情形，相间动量，κ、ε源项不包含在计算中---In most cases these terms

can be neglected。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。

通用多相流的边界条件 1）vof model

For an exhaust fan, inlet vent, intake fan, outlet vent, pressure inlet, pressure outlet, or velocity inlet, there are no

conditions to be specified for the primary phase. For each secondary phase, you will need to set the volume fraction as a

constant, a profile (see Section 7.26: Boundary Profiles), or a user-defined function (see the separate UDF Manual). All

other conditions are specified for the mixture.

For a mass flow inlet, you will need to set the mass flow rate or mass flux for each individual phase. All other conditions are specified for the mixture.

For an axis, fan, outflow, periodic, porous jump, radiator, solid, symmetry, or wall zone, all conditions are specified

for the mixture; there are no conditions to be set for the individual phases.

For a fluid zone, mass sources are specified for the individual phases, and all other sources are specified for the mixture.

2)Mixture Model

For an exhaust fan, outlet vent, or pressure outlet, there are no conditions to be specified for the primary phase. For

each secondary phase, you will need to set the volume fraction. All other conditions are specified for the mixture.

For an inlet vent, intake fan, or pressure inlet, you will specify for the mixture which direction specification method

will be used at this boundary (Normal to Boundary or Direction Vector). If you select the Direction Vector specification

method, you will specify the coordinate system (3D only) and flow-direction components for the individual phases. For each

secondary phase, you will need to set the volume fraction (as described above). All other conditions are specified for the mixture.

For a mass flow inlet, you will need to set the mass flow rate or mass flux for each individual phase. All other conditions are specified for the mixture.

Note that if you read a mixture multiphase case that was set up in a version of FLUENT previous to 6.1, you will need to

redefine the conditions at the mass flow inlets.

For a velocity inlet, you will specify the velocity for the individual phases. For each secondary phase, you will need to

set the volume fraction (as described above). All other conditions are specified for the mixture. For an axis, fan, outflow, periodic, porous jump, radiator, solid, symmetry, or wall zone, all conditions are specified

for the mixture; there are no conditions to be set for the individual phases. Outflow boundary conditions are not available for the cavitation model.

For a fluid zone, mass sources are specified for the individual phases, and all other sources are specified for the mixture.

3) Eulerian Model

For an exhaust fan, outlet vent, or pressure outlet, there are no conditions to be specified for the primary phase if you

are modeling laminar flow or using the mixture turbulence model (the default multiphase turbulence model), except for

backflow total temperature if heat transfer is on. For each secondary phase, you will need to set the volume fraction. If

you are using the mixture turbulence model, you will need to specify the turbulence boundary conditions for the mixture; if

you are using the dispersed turbulence model, you will need to specify them for the primary phase; if you are using the

per-phase turbulence model, you will need to specify them for the primary phase and for each secondary phase. All other

conditions are specified for the mixture.

For an inlet vent, intake fan, or pressure inlet, you will specify for the mixture which direction specification method

will be used at this boundary (Normal to Boundary or Direction Vector). you will also need to set the total temperature for

the individual phases. For each secondary phase, you will need to set the volume fraction. If you are using the mixture

turbulence model, you will need to specify the turbulence boundary conditions for the mixture; if you are using the dispersed

turbulence model, you will need to specify them for the primary phase; if you are using the

per-phase turbulence model,

you will need to specify them for the primary phase and for each secondary phase. All other conditions are specified for the mixture.

For a velocity inlet, you will specify the velocity for the individual phases. If heat transfer is on, you will also need

to set the total temperature for the individual phases. For each secondary phase, you will need to set the volume fraction

(as described above). If the phase is granular, you will also need to set its granular temperature. If you are using the

mixture turbulence model, you will need to specify the turbulence boundary conditions for the mixture; if you are using the

dispersed turbulence model, you will need to specify them for the primary phase; if you are using the per-phase turbulence

model, you will need to specify them for the primary phase and for each secondary phase. All other conditions are specified for the mixture.

For an axis, outflow, periodic, solid, or symmetry zone, all conditions are specified for the mixture; there are no

conditions to be set for the individual phases.

For a wall zone, shear conditions are specified for the individual phases; all other conditions are specified for the

mixture, including thermal boundary conditions, if heat transfer is on.

For a fluid zone, all source terms and fixed values are specified for the individual phases, unless you are using the

mixture turbulence model or the dispersed turbulence model. If you are using the mixture turbulence model, source terms and

fixed values for turbulence are specified instead for the mixture; if you are using the dispersed turbulence model, they

are specified only for the primary phase.

通用模型初始化:you often must patch the value for special region.

Inputs for Compressible VOF and Mixture Model Calculations

Only one of the phases can be defined as a compressible ideal gas (i.e., you can select the ideal gas law for the density

of only one phase's material). There is no limitation on using compressible liquids using user-defined functions.

If you are using the VOF model, for stability reasons, it is better (although not required) if the primary phase is a compressible ideal gas.

If you specify the total pressure at a boundary (e.g., for a pressure inlet or intake fan) the

specified value for

pressure at that boundary will be used as total pressure for the compressible phase, and as static pressure for the other

phases (which are incompressible).

For each mass flow inlet, you will need to specify mass flow or mass flux for each individual phase.

通用多相流的求解策略

Solution Strategies for the VOF Model

1) defining reference pressure location：The position that you choose should be in a region that will always contain the

least dense of the fluids (e.g., the gas phase, if you have a gas phase and one or more liquid phases).Thus in systems

containing air and water, for example, it is important that the reference pressure location be in the portion of the domain

filled with air rather than that filled with water.

2)Pressure Interpolation Scheme: For all VOF calculations, you should use the body-force-weighted pressure interpolation scheme or the PRESTO! scheme.

3)Discretization Scheme Selection for the Implicit and Euler Explicit Formulations:When the implicit or Euler explicit

scheme is used you should use the modified HRIC, second-order, or QUICK discretization schemes for the volume fraction

equations in order to improve the sharpness of the interface between phases.

4)Pressure-Velocity Coupling and Under-Relaxation for the Time-Dependent Formulations:The PISO scheme is recommended

for transient calculations in general. Using PISO allows for increased values on all under-relaxation factors, without a

loss of solution stability. You can generally increase the under-relaxation factors for all variables to 1 and expect

stability and a rapid rate of convergence (in the form of few iterations required per time step). For calculations on

tetrahedral or triangular meshes, an under-relaxation factor of 0.7~0.8 for pressure is recommended for improved stability with the PISO scheme.

5)Under-Relaxation for the Steady-State Formulation:If you are using the steady-state implicit VOF scheme, the

under-relaxation factors for all variables should be set to values between 0.2 and 0.5 for improved stability.

Solution Strategies for the mixture Model

1)Setting the Under-Relaxation Factor for the Slip Velocity:You should begin the mixture calculation with a low

under-relaxation factor for the slip velocity. A value of 0.2 or less is recommended. If the solution shows good convergence

behavior, you can increase this value gradually.

2)For some cases (e.g., cyclone separation), you may be able to obtain a solution more quickly if you compute an initial

solution without solving the volume fraction and slip velocity equations(In the Solution Controls panel, deselect Volume

Fraction and Slip Velocity in the Equations list).

Solution Strategies for the Euler Model 1)Calculating an Initial Solution:

Set up and solve the problem using the mixture model (with slip velocities) instead of the Eulerian model. You can then

enable the Eulerian model, complete the setup, and continue the calculation using the mixture-model solution as a starting point.

Set up the Eulerian multiphase calculation as usual, but compute the flow for only the primary phase. To do this,

deselect Volume Fraction in the Equations list in the Solution Controls panel. Once you have obtained an initial solution

for the primary phase, turn the volume fraction equations back on and continue the calculation for all phases.

2)Temporarily Ignoring Lift and Virtual Mass Forces

3)Using W-Cycle Multigrid:For problems involving a packed-bed granular phase with very small particle sizes (on the order

of 10 μm), convergence can be obtained by using the W-cycle multigrid for the pressure. Under Fixed Cycle Parameters in

the Multigrid Controls panel, you may need to use higher values for Pre Sweeps, Post Sweeps, and Max Cycles. When you are

choosing the values for these parameters, you should also increase the Verbosity to 1 in order to monitor the AMG performance

; i.e., to make sure that the pressure equation is solved to a desired level of convergence within the AMG solver during each global iteration.

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