ansysFLUENT物理模型剖析

ANSYS

FLUENT培训教材第八节：物理模型A

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China安世亚太科技（北京）有限公司概要多相流模型Discrete

phase

modelEulerian

modelMixture

modelVolume-of-fluid

model化学反应模型Eddy

dissipation

modelNon-premixed,

premixed

and

partially

premixed

combustion

modelsDetailed

chemistry

modelsPollutant

formationSurface

reactions动网格Single

and

multiple

reference

framesMixing

planesSliding

meshesDynamic

meshesSix-degree-of-freedom

solverA

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China多相流模型A

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China简介相具有可定义的边界，对周围流场有特定的动力响应相一般分为固体、液体和气体，但也指其他形式：有不同化学属性的材料，但属于同一种物理相（如液-液）多相流体系统分为一种主流体相和多种次流体相其中一种流体是连续的（主流体）其他相是离散的，存在于连续相中可以有多种次流体相，代表不同尺寸的颗粒Primary

PhaseSecondary

phase(s)A

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China多相流体系气泡流–连续液体中存在离散的气泡，如气体吸收器，蒸发设备，鼓泡设备液滴流–连续气体中的离散液滴，如喷雾器、燃烧器柱塞流–连续液体中的大尺度气泡分层/自由表面流–不相溶的流体被清晰的界面分开，如自由表面流颗粒流–连续气体中的离散固体颗粒，如旋风分离器，空气净化器，吸尘器流化床–流化床反应器泥浆流–液体中的固体颗粒，固体悬浮、沉积、液力输运气/液液/液气/固液/固Fluidized

BedSedimentationStratified

/

Free

-Pneumatic

Transport,Surface

Flow

Hydrotransport,

or

Slurry

FlSlug

FlowBubbly,

Droplet,

orParticle-

Laden

FlowA

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ChinaFLUENT中的多相流模型FLUENT包括四种不同的多相流模型:Discrete

Phase

Model

(DPM)Volume

of

Fluid

Model

(VOF)Eulerian

ModelMixture

Model选择合适的模型非常重要取决于流体是分层的还是离散的-两相间的长度尺度界定这个区别Stokes数(颗粒松弛时间和流体特征时间的比例）也应该考虑进来where

and

.A

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ChinaDPM例子-喷雾干燥喷雾干燥包括液体以雾状方式喷入加热的容器中，用DPM模拟流动、传热、传质过程ContoursofEvaporatedWaterStochastic

ParticleTrajectories

for

Different

Initial

DiametersInitial

particleDiameter:

2

mm1.1

mm 0.2

mmA

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China欧拉模型的例子–三维气泡床Liquid

Velocity

VectorsIsosurface

of

GasVolume

Fraction

=

0.175z

=

5

cmA

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Chinaz

=

10

cmz

=

15

cmz

=

20

cm欧拉模型中的粒状选项当存在高浓度的固体颗粒时，会导致颗粒间高频率的碰撞，此时应选Granular假设颗粒的行为类似一团密集分子的碰撞行为，对颗粒相使用分子云理论应用这个理论后，连续相和颗粒相的动量方程都增加了附加应力这些应力(颗粒“粘性”,“压力”等.)由颗粒速度脉动强度确定伴随颗粒速度脉动的动能由拟热

“pseudo-thermal”或颗粒温度代表不考虑颗粒的弹性变形Contours

of

Solids

VolumeFraction

for

High

VelocityGas/Sand

ProductionGas

/

SandGasGravityA

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China混合模型案例–气体鼓泡用混合模型模拟氮气喷入混合器中的流动，用MRF方法模拟旋转

叶片的效应FLUENT很好的模拟了气体的停顿和搅动过程。Animation

of

GasVolumeFractionContoursWater

Velocity

Vectors

onaCentral

Plane

att

=

15

sec.A

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ChinaVOF案例–汽车油箱晃动模拟不同加速条件下，液体在汽车油箱中的

自由液面晃动模拟显示油箱底部的挡板可以保持入油口浸没在油中，如果没有挡板时，入油口在某些时间会露出油面Fuel

Tank

Without

Bafflest

=

1.05

sect

=

2.05

secA

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ChinaFuel

Tank

With

Baffles化学反应流A

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ChinaLet’s

go

ahead

and

get

started

withan

introductory

discussion

of

combustionmodels

and

the

different

kinds

of

tools

that

are

withinFluent

tohandle

combustion

applications.

There’s

a

wide

rangeof

problems

that

can

be

handled

by

the

Fluent

software

for

homogeneousas

well

asheterogeneous

reacting

flows

that

you

might

find,

for

example,

in

furnaces,

boilers,

process

heaters,

gas

turbines

and

rocket

engines.

So,

typically,

people

who

are

usingour

code

for

these

kinds

of

applications

are

interested

in

a

number

of

different

results.

They’re

interested

in

looking

at

the

flow

field

and

the

mixing

characteristics

for

fuel

and

oxidizer

within

their

application.

They’re

also

interested

in

the

temperature

fieldto

answer

question

like:

Is

the

temperature

uniform?

Are

there

hot

spots?

What’s

the

maximumtemperature

withinthe

device?

They’re

lookingat

species

concentrations,

and

in

particular,

oftentimes

people

are

interested

inlookingat

pollutant

emission,

like

NOX,

and

at

particulatedispersion.So

there’s

awide

range

of

interests

by

people

that

are

using

our

software

for

combustion

modeling

and

we

have

avariety

of

physical

models

andtools

available

to

handle

these

problems.Temperature

in

a

GasFurnaceCO2

Mass

FractionStream

Function化学反应流的应用FLUENT包含了从计算均相反应到非均相反应的多个反应模型炉子锅炉热处理炉燃气轮机火箭发动机内燃机–CVD, 化反应反应流一般预测流动和混合温度组分浓度颗粒和污染A

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ChinaSo

we’re

looking

for

practical

approaches

to

deal

with

these

reaction

rates

in

turbulent

flows.

So,

you

can

use

reduced

chemicalmechanisms

andthat’s

what

is

done

in

the

finite

rate

combustion

model.

We

can

also

decouple

the

chemistry

from

the

turbulent

flow

and

mixing

problemand

we

do

that

with

the

PDF

model

and

the

laminar

flamelet

model.

We

can

also

utilize

what’s

calleda

progress

variable

to

perform

this

decoupling,

andthat’s

what’s

the

Zimont

model

is

about.

We’ll

take

a

look

at

each

of

these

models

in

more

detail

later

on.背景知识模拟燃烧中的化学反应快速化学反应全局化学反应机理（有限速率/涡耗散）平衡/小火焰模型（混合分数）–有限速率反应流动结构非预混反应系统可简化为混合系统预混反应系统冷态反应物传播到热的生成物中.FuelOxidizerReactorOutletFuel+OxidizerReactorOutletFuel+OxidizerReactorSecondary

Fuel

or

OxidizerA

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ChinaOutlet化学反A

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China应流动结构PremixedNon-PremixedPartiallyPremixedFastChemistryEddy

Dissipation

Model(Species

Transport)PremixedCombustionModelNon-PremixedEquilibriumModelPartially

PremixedModelReactionProgressVariable*MixtureFractionReaction

ProgressVariable+Mixture

FractionFinite-RateChemistryLaminar

Flamelet

ModelLaminar

Finite-Rate

ModelEddy-Dissipation

Concept

(EDC)

ModelComposition

PDF

Transport

ModelFLUENT中反应流模型污染物模型A

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ChinaNOx形成模型（预测定性的

NOx形成趋势）FLUENT包括三种NOx产生机理Thermal

NOxPrompt

NOxFuel

NOxNOx还原模型选择性非催化还原模型(SNCR)

l喷入氨水或尿素烟灰形成模型Moos-Brookes模型一步模型，两步模型烟灰对辐射吸收的影响SOx形成模型求解SO2,

H2S,或者SO3方程一般SOx预测都作为后处理过程来进行DPM模型描述颗粒/液滴/气泡的轨迹在拉格朗日坐标系求解颗粒和连续相可以进行热、质量、动量的交换每一条轨迹代表一组有相同初始属性颗粒的行为单个颗粒的互相影响被忽略离散相体积分数必须小于10多个子模型离散相的加热/冷却液滴的蒸发和沸腾可燃固体的挥发分析出和焦炭燃烧喷雾模型模拟液滴破碎和聚合磨损/增长应用范围颗粒分离、分级、喷雾干燥、浮质沉积、气泡喷射、液体燃料和煤粉燃烧.A

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China表面反应A

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China对于化学组分沉积到表面的反应，将沉积的组分处理为和气相组分不同的另外一种组分对每个吸收表面组分求解地点平衡方程可以考虑详细表面反应机理（任意的多步反应，任意数量的气相组分/沉积组分）CHEMKIN中的表面反应机理可以读入FLUENT.表面反应可以在壁面或多孔介质中发生可以在不同的表面定义不同的表面反应机理应用案例催化反应CVD（化学沉积）总结对反应流动，有四个基础的教程组分传输和气相燃烧非预混燃烧表面化学反应液滴挥发A

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China动网格A

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ChinaComputationalfluid

dynamics

(or

CFD)

has

been

used

to

examine

problems

involving

moving

domains

ever

since

the

advent

of

computersimulation

in

the

1960s.

The

motions

can

either

be:Translational

–

such

as

the

cyclic

oscillation

of

liquid

in

atank

or

atrain

moving

through

atunnel.OrRotational

–

whichis

perhaps

the

most

common.

Examples

include

flows

though

turbomachines

(pumps,

turbines,

compressors,

and

relatedequipment),

electric

motors,

spinning

objects

such

as

car

tires,

and

so

forth.There

are

two

basic

approaches

to

modeling

flows

in

moving

domains.The

first

approach

involves

referring

the

problemtoa

moving

reference

frame.

For

example,

we

can

define

a

reference

frame

which

is

spinning

in

concertwith

a

rotating

tank.

The

flow

is

described

with

respect

to

the

spinning

reference

frame.

However,

the

fact

that

the

reference

frame

itself

is

moving

gives

rise

to

“non-inertial”

effects

–

that

is,

the

equations

of

motion

now

have

additional

acceleration

terms

added

to

themto

accountfor

the

moving

frame

(more

aboutthat

later).The

benefit

of

using

a

moving

reference

frame

is

often

a

problemwhich

is

inherently

unsteady

in

the

stationary

frame

becomessteady-state

in

the

moving

frame

of

reference.

Moreover,

we

can

couple

adjacentzone

to

the

moving

zone

though

grid

interfaces

tocreate

a

simplified

model

of

a

complex

moving

zone

system

(forexample

a

pump

impeller

coupled

with

a

scroll

casing).The

second

approach

solves

the

equations

using

a

meshwhich

is

moving

with

respect

to

a

fixed

frame,

and

we

refer

all

flowvariables

to

the

fixedframe.

In

this

case,

the

solution

is

inherently

unsteady.

The

main

advantage

of

this

approach

is

that

we

can

allow

the

mesh

(and

hence

the

domain)

to

deformwithtime,

thus

permitting

a

wide

range

of

problems

involving

moving

and

deforming

boundaries.动网格简介许多问题需要考虑平移或旋转的部件对移动域，有两种基本的模型方法:运动的参考坐标系参考坐标系和运动域联系在一起修正控制方程来考虑运动坐标系运动/变形域域的位置和形状在静止坐标系下跟踪求解本质上是瞬态的A

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China运动域的CFD模型方法单参考坐标系(SRF)多参考坐标系(MRF)混合平面法(MPM)滑移网格

(SMM)运动坐标系A

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China运动域运动/变形网格(MDM)The

single

reference

frame

model

is

the

simplest

approach

for

moving

zone

modeling.

In

this

approach,

a

single,

non-deformingfluid

domain

isreferred

to

amoving

frame

of

reference.

As

mentioned

previously,

the

equationsof

motion

are

modified

to

account

for

the

non-inertial

motionofthe

moving

frame.

In

addition,

boundary

conditions

are

defined

relative

to

the

moving

zone.Why

use

a

rotatingframe

to

begin

with?

The

reason

is

that,

for

many

common

classes

of

moving

zone

problems,

a

flowfield

which

is

unsteadywhen

viewed

from

the

stationary

frame

becomes

steady

in

the

moving

frame.

Steady-state

problems

are

desirable

as

they

are

(1)

easier

and

lessexpensive

to

solve,

(2)

possess

simpler

BCs,

and

(3)

are

more

straightforward

to

post-process

and

analyze.Please

note

that

you

may

still

model

natural

unsteadiness

in

the

moving

frame

–

for

example,

vortex

shedding

from

the

trailing

edge

of

arotatingfan

blade.Now,

when

you

model

a

rotating

zone

with

the

SRF

approach,

it

is

important

to

note

that

the

walls

must

conformto

the

following

requirements:Walls

which

move

withthe

reference

frame

can

be

any

shape

(3-D)Walls

whichare

to

modeled

as

stationary

(with

respect

to

the

fixed

frame)

must

be

surfaces

of

revolution!

If

your

domain

does

not

meet

thisrequirement,

you

must

break

your

model

up

into

multiple

zones

and

use

an

approach

which

supports

multiple

zones.Finally,

it

is

very

common

to

employ

rotationally

periodic

boundaries

in

SRF

models

as

it

reduces

the

mesh

size

froman

entire

rotating

geometryto

a

single

periodic

passage.

Of

course,

both

your

geometry

and

your

flowfield

must

be

rotationally

periodic,

whichcan

be

an

issue

if,

forexample,

your

inflow

BC

is

not

periodic.单参考坐标系模型(SRF)SRF把单一的运动域和一个坐标系连接起来所有的流体域在运动坐标系下定义旋转坐标系引入了附件加速度为什么要使用运动坐标系?在静止坐标系下流场是瞬态的，使用旋转坐标系后流场可以看做稳态的优势用稳态方法求解*边界条件更简单调试更快捷更容易的后处理的分析CentrifugalCompressor(single

blade

passage)A

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China*注意:在旋转坐标系下有时依然有瞬态现象，如湍流、周期非平衡、分离、涡脱落等There

are

many

moving

zone

problems

which

cannot

be

solved

using

the

SRF

approach

alone

–

specifically,

applications

with

stationarycomponents

with

wallsthat

are

notsurfaces

of

revolution.

For

example,

a

centrifugal

pump

impeller

typically

is

situated

next

to

a

scroll-shaped

casing

or

volute.

Since

the

casing

is

nota

surface

or

revolution

aboutthe

axis

of

rotation,

you

cannot

include

that

region

in

the

moving

reference

frame

zone.To

address

these

kinds

of

problems,

you

must

break

up

the

domaininto

multiple

fluid

zones,

some

which

are

moving

and

others

which

arestationary.

The

zones

communicate

across

one

or

more

interfaces,

therebypermitting

a

specific

degree

of

interaction

between

the

zones.

The

wayin

which

the

interface

is

treated

leads

to

one

of

the

following

multiple

zone

approaches:The

multiple

reference

frame

modelThe

mixing

plane

modelThe

sliding

mesh

model多参考坐标系模型(MRF)包括有静止域和运动域的多域问题此时，单参考坐标系不适合，为这类系统可以这样处理：把域分割多个域：一些域旋转，一些域静止域之间通过交界面传递数据对交界面的处理方式分为以下几种：多参考坐标系模型(MRF)混合平面模型(MPM)滑移网格模型(SMM)interfaceMultiple

Component(blower

wheel

+

casing)稳态（近似）瞬态（精确）A

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ChinaThe

mixing

plane

model

isamethod

which

was

developed

within

the

turbomachinery

community

as

a

way

of

dealingwith

multiple

blade

rowcompressor

and

turbine

analyses.

It

has

since

become

more

widely

applied

to

pumps,

fans,

and

similar

systems.The

basic

idea

is

to

consider

a

systemof

single

passage,

SRF

models

whichare

aligned

such

that

the

outlet

of

an

upstreamzone

feeds

the

inlet

of

a

downstreamzone.

We

can

obtain

a

steady-state

solution

to

this

system

in

the

following

manner.

First,

we

establishlinks

between

adjacentboundary

conditions

so

that

flow

data

fromone

domain

is

passed

as

a

boundary

condition

to

the

adjacent

zone.

We

then

obtain

a

provisionalsolution

in

each

SRF

zone

in

the

usual

way.

At

the

end

of

the

solution

step,

we

average

the

flow

propertiesatthe

interface

flow

boundaries

in

thecircumferential

direction,

thereby

obtaining

asimple

radial

or

axial

profile.

Profiles

are

create

for

each

variable

required

by

the

adjacent

zone’sboundary

condition.

These

profiles

are

then

applied

to

the

adjacent

zones

(much

like

one

would

apply

a

profile

file

toa

standard

Fluentmodel).

Bycontinuouslyupdating

the

boundary

conditions

in

this

fashion,

a

coupled,

steady-state

flow

solution

will

be

obtained

at

convergence.混合平面模型(MPM)MPM方法是对多级轴流和离心旋转机械的稳态解法也适用于其他一般问题域有多个单通道、旋转或静止流体域组成每个域有自己的进口、出口、壁面和周期边界（每个域是一个SRF模型）对每个域求解稳态的

SRF，通过边界条件链接各个域链接域的边界称为混合平面通过混合平面的变量是周向平均值，随每步迭代更新分布可以是径向或轴向求解收敛后，混合平面将调整为一般流动条件Mixing

plane

(Pressure

outlet

linked

witha

mass

flow

inlet)A

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ChinaMPM的优势:只需要一个流道，和叶片数量无关In

the

MRF

and

mixing

plane

approaches,

we

assume

that

interactions

between

components

are

weak

and

therefore

could

be

neglected

in

theanalysis.

This,

of

course,

is

clearly

an

approximation.

The

motion

of

a

moving

blade,

for

instance,

pasta

stationary

vane

will

give

riseto

unsteadyinteractionsas

shown

in

this

slide.

These

interactions

can

be

classified

as

follows:First

we

have

potential

interactions

(or

pressure

waves).

These

are

a

result

of

hydrodynamic

interactions,

and

are

a

two-way

effect

–

that

is,

thewaves

are

felt

both

upstreamand

downstream.Next

we

wake

interactions,

which

arearesultof

wakes

fromupstreamobjects

impacting

downstreamcomponents.

Unlike

potential

interactions,this

is

a

one-way

effect.If

the

flow

is

compressible

and

Mach

numbers

are

high

enough,

we

may

also

have

shock

wave

interactions.

Like

wake

effects,

this

is

a

one-wayinteraction.If

the

components

are

sufficiently

remove

fromone

another,

these

interaction

effects

are

small

and

can

often

be

ignored,

thus

permitting

the

use

ofMRFor

mixing

plane

techniques.

However,

interaction

between

closely

spaced

components

is

usually

very

large

and

cannotbe

ignored.

Inaddition,

there

can

be

complexflows

occurring

in

the

vicinity

of

the

interfaces

between

moving

and

non-moving

zones

such

that

the

MRF

or

mixing

plane

models

will

be

sensitive

to

the

interface

location.When

interaction

effects

cannot

be

ignored,

we

can

employ

the

sliding

meshmodel

to

simulate

the

unsteady

interaction

effects.滑移网格模型(SMM)旋转机械中，静止部件和旋转部件的相对运动导致瞬态相互作用，一般分为以下几种：位差相互作用(压力波相互作用)尾迹相互作用激波相互作用MRF和MPM模型都忽略了瞬态相互作用，仅限于瞬态效应小的流动如果瞬态效应不能忽略，可以使用SMM方法考虑静止部件和旋转部件的相对运动wake

interactionShockinteractionpotentialinteractionStatorRotorA

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slidingmeshmodel

can

be

thought

of

as

an

extension

of

the

MRF

approach,

in

that

we

define

stationary

and

moving

zones

separated

by

non-conformal

interfaces.

As

the

calculation

proceeds,

the

moving

zone

meshes

are

updated

as

a

function

of

time,

thereby

making

the

probleminherently

unsteady.

Itshould

be

noted

that

the

meshes

are

moved

in

arigid

(non-deforming)

manner

and

communication

with

adjacent

zones

willbe

maintained

provided

the

grid

interfaces

maintain

an

overlap

with

one

another

(hence

the

name

sliding

mesh).Another

difference

that

the

sliding

mesh

model

has

with

MRF

is

the

equations

that

areused.

In

the

sliding

mesh

model,

a

moving

mesh

formulationis

used

whichrefers

all

flow

variables

to

the

stationary

or

inertial

frame,

and

solves

for

absolute

quantities.

More

details

about

thisformulationare

provided

in

the

Appendix.

The

primaryimplication

is

that,

unlike

SRF,

MRF,

and

MPM,

the

momentumequations

do

not

containCoriolis

and

centripetal

acceleration

terms

–

however,

the

geometry

(mesh)

is

now

a

function

of

time,

which

wasn’t

the

case

with

the

MovingReference

Frame

approach.

It

should

also

be

noted

that

the

equations

employed

for

sliding

mesh

models

are

a

special

case

of

the

generalmoving/deforming

mesh

formulation

which

assumes

rigid

mesh

motion

and

sliding,

non-conformal

interfaces.SMM模型如何工作另一个和

MRF模型不同之处是，控制方程有新的动网格形式，在静止坐标系下求解绝对量没有使用运动坐标系形式（例如，动量方程源项中没有附加加速度的作用）方程组是通用的运动/变形网格形式的一种特殊情况假设为刚性网格运动和滑移，非一致网格界面cells

at

time

tcells

at

time

t

+

Δt和MRF模型类似的是，计算域分为运动域和静止域，由非一致网格界面连接和MRF模型不同的是，每个域的网格是时间的函数，随时间改变，这样使得问题本身就是瞬态的。moving

mesh

zoneA

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dynamic

mesh

model

in

Fluent

is

comprisedof

a

“toolbox”

of

methods

for

controlling

the

mesh

motion.

There

are

three

general-purposemethods

for

dealingwith

mesh

deformations,

and

these

are:SpringanalogyLocal

RemeshingLayeringFor

specific

classes

of

mesh

motion

and

geometries,

there

are

the

several

specialized

approaches,

specifically:The

2.5D

methodThe

user-defined

mesh

motion

approachThe

in-cylinder

motion

package

(design

with

automotive

in-cylinder

applications

in

mind)The

6

degree-of-freedom

packageIt

should

be

noted

that

these

schemes

are

very

flexible,

and

one

can

utilize

more

than

one

approach

in

a

single

model,

including

the

use

ofstationary

and

sliding

non-conformal

interfaces.

We

will

show

anexampleof

this

ability

in

a

later

slide.动网格方法(DM)A

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China内部节点位置随着边界的运动自动计算基本格式弹簧式(光顺)局部重新划分层铺式其他方法2.5

D用户定义网格运动内燃机网格运动(RPM,

stroke

length,

crank

angle,…)通过分布或UDF预先定义的运动通过6DOF求解器，把流场求解的气动力和运动耦合起来动网格方法层铺法随着边界的移动，单元层生成或消失。单元层可以是四边形/六面体/四面体类型，适合边界在小范围或大范围内的线性或旋转运动局部重划法随着边界移动，网格扭曲大的区域网格重新划分。适用于三角形/四面体网格类型，边界运动范围大。弹簧式弹簧式适用于小范围的边界变形，单元的连接和数量不变，弹簧式适用于小范围变形的三角形/四面体网格A

Pera

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Company

©

PERA

ChinaThe

dynamic

meshmodel

is

the

name

given

to

a

generalmodeling

framework

whichpermits

flow

solutions

in

arbitrarily

moving

and

deformingdomains.

The

user

defin