CFD ( computation flow diagram)

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Introduction to Computational Fluid

Dynamics

CFD Introduction


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CFD 2

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!at is Computational Fluid Dynamics"

Computational Fluid Dynamics #CFD$ is t!e science o% predictin&

%luid %lo'( !eat trans%er( mass trans%er( c!emical reactions( and related

p!enomena )y sol*in& t!e mat!ematical e+uations '!ic! &o*ern t!ese

processes usin& a numerical process #t!at is( on a computer$,

!e result o% CFD analyses is rele*ant en&ineerin& data used in. conceptual studies o% ne' desi&ns

detailed product de*elopment

trou)les!ootin&

redesi&n

CFD analysis complements testin& and eperimentation, Reduces t!e total e%%ort re+uired in t!e la)oratory,

Courtesy. Fluent( Inc,


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CFD

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pplications

pplications o% CFD are numerous %lo' and !eat trans%er in industrial processes #)oilers( !eat ec!an&ers(

com)ustion e+uipment( pumps( )lo'ers( pipin&( etc,$

aerodynamics o% &round *e!icles( aircra%t( missiles %ilm coatin&( t!ermo%ormin& in material processin& applications

%lo' and !eat trans%er in propulsion and po'er &eneration systems

*entilation( !eatin&( and coolin& %lo's in )uildin&s

c!emical *apor deposition #C3D$ %or inte&rated circuit manu%acturin&

!eat trans%er %or electronics pac4a&in& applications and many( many more,,,



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CFD

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CFD - o' It or4s

nalysis )e&ins 'it! a mat!ematical model

o% a p!ysical pro)lem, Conser*ation o% matter( momentum( and

ener&y must )e satis%ied t!rou&!out t!e

re&ion o% interest, Fluid properties are modeled empirically,

impli%yin& assumptions are made in order

to ma4e t!e pro)lem tracta)le #e,&,( steady-

state( incompressi)le( in*iscid( t'o-

dimensional$, 8ro*ide appropriate initial and/or )oundary

conditions %or t!e pro)lem,

Domain %or )ottle %illin&

pro)lem,

Fillin&

No99le

:ottle



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CFD 6

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n =ample. ater %lo' o*er a tu)e )an4

;oal compute a*era&e pressure drop( !eat

trans%er per tu)e ro'

ssumptions %lo' is t'o-dimensional( laminar(

incompressi)le

%lo' approac!in& tu)e )an4 is steady

'it! a 4no'n *elocity

)ody %orces due to &ra*ity are ne&li&i)le

%lo' is translationally periodic #i,e,

&eometry repeats itsel%$

8!ysical ystem can )e modeled'it! repeatin& &eometry,



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CFD 7

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CFD codes are structured around t!e numerical al&orit!ms t!at can tac4le%luid %lo' pro)lems

!ree main elements.

1, 8re 8rocessor

2, ol*er

, 8ost 8rocessor

How Does a CFD Code Work?


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CFD >

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Consists o% t!e input o%

a %lo' pro)lem to CFD ?ser cti*ities.

de%ine &eometry @ &enerate &rid #50A

time$

selection o% p!enomena to )e modeled

de%inition o% %luid properties speci%ication o% )oundary and initial

conditions

1) Pre-Processor


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CFD B

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!ree primary numerical solution tec!ni+ues

%inite di%%erence( %inite element( %inite control *olume

!e numerical met!od per%orms t!e %ollo'in&.

pproimates t!e un4no'n *aria)les )y simple %unctions Discreti9ation )y su)stitution o% t!e approimations into t!e

&o*ernin& %lo' e+uations and su)se+uent mat!ematical

manipulations

olution o% t!e al&e)raic e+uations

2) Solver


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CFD 10

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Finite di%%erence met!ods descri)e t!e un4no'ns φ o% t!e %lo'

pro)lems )y means o% point samples at t!e node points o% a &rid

co-ordinate lines

Solver - Finite Difference Method

Truncated Taylor series epan-sions are used to

&enerate %inite di%%erence approimations o% t!e

deri*ati*es o% φ in terms o% point samples o% φ ateac! &rid point and its immediate nei&!)ors


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CFD 11

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8ro*ides a user %riendly #""$ 'ay to loo4 at t!e results o% a simulation

Domain &eometry and &rid display 3ector 8lots

Contour 8lots

8article rac4in&

3) Post Processor


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CFD 12

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Results o% CFD are at )est as &ood as t!e physics em)edded in it as at 'orst as&ood a its operator

== 8RE:=


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CFD 1

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d*anta&es o% CFD

Low Cost

?sin& p!ysical eperiments and tests to &et essential en&ineerin& data %or

desi&n can )e epensi*e,

Computational simulations are relati*ely inepensi*e( and costs are li4ely to

decrease as computers )ecome more po'er%ul, Speed

CFD simulations can )e eecuted in a s!ort period o% time,

Huic4 turnaround means en&ineerin& data can )e introduced early in t!e

desi&n process

Ability to Simulate Real Conditions


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CFD 1

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d*anta&es o% CFD #2$ Ability to Simulate Ideal Conditions

CFD allo's &reat control o*er t!e p!ysical process( and pro*ides t!e a)ility to

isolate speci%ic p!enomena %or study,

=ample. a !eat trans%er process can )e ideali9ed 'it! adia)atic( constant !eat

%lu( or constant temperature )oundaries,

Comprehensive Inormation

=periments only permit data to )e

etracted at a limited num)er o%

locations in t!e system #e,&, pressure

and temperature pro)es( !eat %lu

&au&es( D3( etc,$ CFD allo's t!e analyst to eamine a

lar&e num)er o% locations in t!e re&ion

o% interest( and yields a

compre!ensi*e set o% %lo' parameters

%or eamination,Courtesy. Fluent( Inc,


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CFD 15

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imitations o% CFD

!hysical "odels CFD solutions rely upon p!ysical models o% real 'orld processes #e,&,

tur)ulence( compressi)ility( c!emistry( multip!ase %lo'( etc,$,

!e solutions t!at are o)tained t!rou&! CFD can only )e as accurate as

t!e p!ysical models on '!ic! t!ey are )ased,

#umerical $rrors

ol*in& e+uations on a computer in*aria)ly introduces numerical errors

Round-o%% error - errors due to %inite 'ord si9e a*aila)le on t!e computer

runcation error - error due to approimations in t!e numerical models

Round-o%% errors 'ill al'ays eist #t!ou&! t!ey s!ould )e small in most

cases$



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CFD 16

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imitations o% CFD #2$

%oundary Conditions

s 'it! p!ysical models( t!e accuracy o% t!e CFD solution is only as

&ood as t!e initial/)oundary conditions pro*ided to t!e numerical model,

=ample. Flo' in a duct 'it! sudden epansion

I% %lo' is supplied to domain )y a pipe( you s!ould use a %ully-de*eloped

pro%ile %or *elocity rat!er t!an assume uni%orm conditions,

poor )etter

Fully De*eloped Inlet

8ro%ile

Computational

Domain

Computational

Domain

?ni%orm Inlet

8ro%ile



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© Ram Ramanan05/27/16CFD 17

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ummary

Computational Fluid Dynamics is a po'er%ul 'ay o% modelin& %luid

%lo'( !eat trans%er( and related processes %or a 'ide ran&e o% important

scienti%ic and en&ineerin& pro)lems,

!e cost o% doin& CFD !as decreased dramatically in recent years( and

'ill continue to do so as computers )ecome more and more po'er%ul,


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CFD ( computation flow diagram)