ws backward step例题04湍流流过台阶

例题04湍流流过台阶介绍例题描述:湍流台阶流动是湍流模型中标准的测试案例。我们将用Fluent建立和求解湍流流动问题，学习用

CFD-Post和Workbench来比较不同的湍流模型结果以及和实验数据做对比。我们还将考察边界条件对结果和影响。学习目标:这个例题包含Fluent中湍流模型很多方面的内容，包括指定模型，近壁面处理，检查Y

PLUS，选择边界条件，比较实验结果和不同湍流模型结果之间的差异。IntroductionModel

SetupSolvingPost-ProcessingSummary仿真目的仿真任务是模拟流体流过台阶。仿真目的:不同的湍流模型结果之间如何比较以及如何跟实验比较模型能否预测台阶下游的回贴点IntroductionModel

SetupSolvingPost-ProcessingSummary启动Fluent并导入网格模型浏览并选择文件“driver.msh.gz”IntroductionModel

SetupSolvingPost-ProcessingSummary显示网格显示网格并放大观察台阶下游底部附近的网格IntroductionModel

SetupSolvingPost-ProcessingSummary激活模型IntroductionModel

SetupSolvingPost-ProcessingSummary打开Viscous

Models

面板并选择Realizable

k-epsilon和Enhanced

Wall

Treatment定义材料如下所示定义空气的density

and

viscosityIntroductionModel

SetupSolvingPost-ProcessingSummary入口边界条件如下所示默认的出口回流设置是足够的，所以不需要再进入到压力出口边界设置Boundary

ConditionsIntroductionModel

SetupSolvingPost-ProcessingSummary在Solution Method面板,

改变‘Pressure-VelocityCoupling’为Coupled

并选择Pseudo

Transient改变pressure为PRESTO!IntroductionModel

SetupSolvingPost-ProcessingSummarySolutionMethodsIn

‘Monitors’,

press

‘Create...’

for

a

Surface

MonitorEnter

‘wall-shear-mon’

for

the

nameCheck

the

box

to

Plot

and

set

the

window

number

to

2Choose

Area-Weighted

Average

for

the

report

typeChoose

Wall

Shear

Stress

for

the

field

variableSelect

bottom_wall

as

the

surfaceMonitorsIntroductionModel

SetupSolvingPost-ProcessingSummaryCreate

another

surface

monitorEnter

‘turb-out-mon’

for

the

nameCheck

the

box

next

to

plot

and

immediately

below

thatset

Window

to

3Select

Area-Weighted

Average

for

the

report

typeSelect

Turbulent

Viscosity

Ratio

for

the

field

variableSelect

outlet_p

in

the

list

of

surfacesMonitorsIntroductionModel

SetupSolvingPost-ProcessingSummaryCalculate

the

SolutionInitialize

the

solution

using

hybrid

initialization,

save

the

project,

and

then

go

to

the

Run

Calculation

panel

and

askfor

100

iterationsThe

residuals

converge

in

a

small

number

of

iterations,

but

the

monitors

do

not

definitively

indicate

that

thesolution

has

stopped

changingIntroductionModel

SetupSolvingPost-ProcessingSummaryContinue

theCalculationSet

the

continuity

residual

criterion

to

1e-6Use

the

TUI

command

/solve/monitors/surface/clear-data

to

clear

the

solution

monitorsIn

the

Run

Calculation

panel,

request

100

more

iterations– Choose

"Use

settings

for

current

calculation

only"IntroductionModel

SetupSolvingPost-ProcessingSummaryJudging

ConvergenceAfter

an

additional

100

iterations,

neither

surface

monitor

is

changing

and

the

residuals

have

all

reached

very

lowlevels– Together,

these

conditions

indicate

the

solution

is

convergedSave

the

project

before

moving

onIntroductionModel

SetupSolvingPost-ProcessingSummaryQuick

Post-Processing:

Wall

YplusPlot

y+

along

the

bottom

wallIntroductionModel

SetupSolvingPost-ProcessingSummaryQuickPost-Processing:

VectorsIntroductionModel

SetupSolvingPost-ProcessingSummaryDisplay

velocity

vectors

and

zoom

in

on

the

step

regionChange

the

turbulence

modelClose

Fluent,

return

to

Workbench

and

save

the

projectIn

the

project

schematic,

right

click

on

the

Fluent

cell

and

rename

it

as

RKERight

click

again

on

the

Fluent

cell

and

select

DuplicateRename

the

duplicate

cell

to

SST

and

Edit

the

setup

block

in

this

cellIntroductionModel

SetupSolvingPost-ProcessingSummarySelect

SST

ModelIn

the

Viscous

Models

panel,

select

the

SST

model

as

shownRepeat

the

steps

performed

in

Slides

12,

13

and

14IntroductionModel

SetupSolvingPost-ProcessingSummaryConvergence（收敛）

is

very

good

both

for

thisproblem

with

both

SST

and

Realizable

k-epsilonYplus

is

qualitatively

similar.

Next

we

will

use

CFDPost

to

make

a

more

quantitative

comparisonSave

the

project,

exit

Fluent

and

return

to

the

ProjectSchematicSST:

Convergence

and

Post-processingIntroductionModel

SetupSolvingPost-ProcessingSummaryFrom

'Component

Systems'

drag

a

'Results'

objectinto

the

Project

SchematicLeft

click

on

the

Solution

cell

for

RKE

(A3)

and

withoutreleasing

the

mouse,

drag

the

pointer

on

top

ofResults

(C2)Repeat

the

previous

step

with

the

Solution

cell

forSST

(B3).

The

Project

Schematic

should

appear

as

tothe

right.Double

click

on

Results

to

start

CFD-PostPost-Processing

in

CFD-PostIntroductionModel

SetupSolvingPost-ProcessingSummaryClick

on

Insert

and

choose

VectorSelect

'symmetry

1'

for

the

location

and

change

thereduction

factor

to

2IntroductionModel

SetupSolvingPost-ProcessingSummaryClick

on

the

Symbol

tab

and

enter

a

value

of

0.5

forSymbol

Size

(not

shown)Zoom

in

on

the

region

just

behind

the

stepVelocity

VectorsExpressionsComparisons

of

results

are

often

made

using

geometrical

coordinates

normalized

by

the

step

height.

This

can

bedone

with

the

help

of

variables

and

expressionsClick

the

Expressions

tab,

then

right

click

and

select

'New'Name

the

expression

'step

height'

and

define

the

expression

ave(Y)@inlet_bottom

-

ave(Y)@bottom_wall

asshown

(below)IntroductionModel

SetupSolvingPost-ProcessingSummaryExpressionsCreate

a

second

expression

for

the

dimensionless

x-coordinate

named

'xh

expression'

as

shown

belowIntroductionModel

SetupSolvingPost-ProcessingSummaryIn

order

to

use

the

previous

expression

to

plot

thewall

shear

stress,

a

variable

needs

to

be

createdClick

the

Variables

tab,

right

click

anywhere

in

thewhite

area,

select

'New'

and

create

a

variable

named'Xh'VariablesIntroductionModel

SetupSolvingPost-ProcessingSummaryPolylineA

polyline

defined

by

the

intersection

of

the

symmetry

boundary

and

the

bottom

wall

is

required

in

order

to

plotthe

wall

shear

stressThere

is

more

than

one

way

to

define

this

polyline,but

the

Boundary

Intersection

method

is

probably

themost

convenient

in

this

case

and

its

use

ensures

thepolyline

definitionwould

remainconsistentif

changeswere

made

upstream

in

the

project

workflow.IntroductionModel

SetupSolvingPost-ProcessingSummarySelect

Insert

>

ChartIn

the

Details

panel,

select

the

polyline

created

in

the

previous

step

in

the

Data

Series

tabSelect

Xh

for

the

X

Axis

variable

and

Wall

Shear

X

for

the

Y

AxisCreate

aChart'Wall

Shear

X'

is

used

instead

of

'Wall

Shear'because

the

location

where

it

changes

signidentifies

the

flowreattachment

point.IntroductionModel

SetupSolvingPost-ProcessingSummaryWall

Shear

Stress

ComparisonIntroductionModel

SetupSolvingPost-ProcessingSummaryThe

resulting

plot

appears

in

the

Chart

ViewerRight

click

in

the

data

field

in

the

chart

details

and

select

"New"Name

the

new

series

"Exp.",

select

File,

navigate

to

the

workshop

files

directory,

change

"Files

of

type"

to

"All

Files(*)"

and

select

x-wall-shear-ds.xyAdd

External

Data

to

ChartIntroductionModel

SetupSolvingPost-ProcessingSummarySelect

the

Line

Display

tab

in

the

chart

details

and

change

the

display

options

as

shown

belowThe

data

appears

on

the

chart

as

seen

to

the

rightPlot

External

DataIntroductionModel

SetupSolvingPost-ProcessingSummaryChanging

the

Inlet

BoundaryConditionRight

click

on

the

RKE

cell

in

the

Project

Schematic

and

select

DuplicateName

the

newly

created

Fluent

object

"RKE

Profile,

right

click

on

the

Setup

cell

and

select

"Edit"IntroductionModel

SetupSolvingPost-ProcessingSummaryNavigate

to

Define

>

Profiles,

select

Read…

in

theProfiles

panel,

navigate

to

the

workshop

filesdirectory

and

select

the

file

"rke-f“Open

the

boundary

conditions

panel

for

the

VelocityInlet

and

use

the

drop

down

arrows

apply

the

profilesas

shown

to

the

rightBe

sure

to

change

the

velocity

specification

methodto

“Components”

and

the

turbulence

specificationmethod

to

"K

and

Epsilon"Adding

ProfilesIntroductionModel

SetupSolvingPost-ProcessingSummaryRunning

the

CalculationInitialize

the

flow

with

hybrid

initialization

and

perform

the

calculation

exactly

as

in

Slides

12-14Good

convergence

behavior

also

with

the

new

boundary

conditionsIntroductionModel

SetupSolvingPost-ProcessingSummaryCheck

theInlet

Velocity

ProfileUse

the

XY

Plot

panel

to

view

the

inlet

profile– Click

on

Axes

and

enable

display

of

grid

lines

for

both

the

X-

and

the

Y-axisAfter

selecting

X

in

the

upper

left

of

the

panel,check

Major

Rules

and

Minor

Rules,

then

clickApply.

Repeat

for

the

Y

axis

and

closethe

panelRemember

to

change

the

Plot

direction

to

(0,1).IntroductionModel

SetupSolvingPost-ProcessingSummaryInlet

Velocity

ProfileThe

profile

is

from

a

developing

boundary

layer

with

freestream

velocity

=

44.2

m/s

and

a

boundary

layerthickness

just

below

2

cm,

as

measured

in

the

experimentIntroductionModel

SetupSolvingPost-ProcessingSummaryIn

the

Project

Schematic,

create

a

duplicate

of

the

SSTFluent

object

and

name

it

SST

ProfileClick

Edit

in

the

Setup

cell

of

the

new

object,

go

toDefine

>

Profiles

and

read

the

profile

"sst-f"Apply

the

profile

at

the

inlet

boundaryInitialize

the

solution

with

Hybrid

Initialization

andrun

the

calculation

using

the

same

steps

described

inSlides

12-14Run

SST

with

Profile

Boundary

ConditionsIntroductionModel

SetupSolvingPost-ProcessingSummaryDuplicating

the

Results

ObjectRight

click

on

the

Results

object

in

the

Project

Schematic

and

select

DuplicateThe

original

calculations

with

uniform

boundary

conditions

are

connected

to

this

cell.

Right

click

on

each

of

theconnections

and

select

DeleteIntroductionModel

SetupSolvingPost-ProcessingSummaryLeft

click

on

the

Solution

cell

for

RKE

Profile

(D3)

andwithout

releasing

the

mouse,

drag

the

pointer

on

topof

Results

with

Profiles

(F2)Repeat

with

SST

Profile

so

that

the

Project

Schematicappears

as

shown–

The

labeling

of

the

individual

blocks

A,B,C,D,…

may

bedifferent

in

your

caseDouble

click

on

Results

with

Profiles

to

launch

CFD-PostExamining

the

New

ResultsIntroductionModel

SetupSolvingPost-ProcessingSummaryDouble

click

on

Chart

1

in

the

Outline

Tree

to

open

the

chartThe

chart

is

automatically

updated

with

the

new

resultsComparing

Results

with

Profile

BCsdefining

variablesBecause

the

original

resultscell

was

duplicated,

none

ofthe

setup

steps

such

asandexpressions

and

loading

theexperimental

data

needed

toberepeatedVery

good

agreement

forthereattachmentpointIntroductionModel

SetupSolvingPost-ProcessingSummaryWrap-upThis

workshop

has

shown

the

steps

for

setting