102627318 design analysis of fan1

8/18/2019 102627318 Design Analysis of Fan1

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DESIGN AND ANALYSIS OF A LOW SPECIFIC SPEED

CENTRIFUGAL FAN

A Dissertation Work Submitted to Jawaharlal NehruTechnological University

In Partial ul!ilment o! the re"uirements o! the award o!

#A$%&'() ( T&$%N('(*+IN

,&$%ANI$A' &N*IN&&)IN*

#y

-.-A)T%I- /0122A/103A.SAI $%A)AN /0122A/13/D.AS%&S% *(PA' NAT% /0122A/1#4

A.S)&&NU /0122A/1#5

De6artment o! ,echanical &ngineering7S)&& NID%I INSTITUT& ( S$I&N$& 8 T&$%N('(*+

+amnam6et7 *hatkesar7 %yderabad95/21/2.

:Accredited by AI$T&7 New Delhi 8 A!!iliated toJNT University7 %yderabad;

http://www.snist.com/Default.aspx


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DESIGN AND ANALYSIS OF A LOW SPECIFIC SPEED

CENTRIFUGAL FAN

A Dissertation Work Submitted to Jawaharlal NehruTechnological University

In Partial ul!ilment o! the re"uirements o! the award o!

#A$%&'() ( T&$%N('(*+IN

,&$%ANI$A' &N*IN&&)IN*

#y

-.-A)T%I- /0122A/103A.SAI $%A)AN /0122A/13/D.AS%&S% *(PA' NAT% /0122A/1#4

A.S)&&NU /0122A/1#5

Under The *uidance o! Dr.,.


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ACKNOWLEDGEMENT

We would take immense 6leasure to acknowledge with gratitude7 the hel6 8 su66ort

e>tended during the course o! our 6ro?ect entitled DESIGN AND ANALYSIS OF A LOW

SPEED CENTRIFUGAL FAN !rom all 6eo6le who have hel6ed in the success!ul

com6letion o! this 6ro?ect.

We are highly indebted to Dr. M.V.S.S.S.M.PRASAD7 Pro!essor7 De6artment o! ,echanical

&ngineering7 !or his guidance and hel6 at all stages o! the 6ro?ect.

We are highly grate!ul to Dr. Ch.SIVA REDDY7 Pro!essor7 %ead o! De6artment o!

,echanical &ngineering !or the !acilities 6rovided to carry out the 6ro?ect.

We are highly thank!ul to Mr. RAVINDER REDDY, Assistant 6ro!essor7 De6artment o!

,echanical &ngineering !or hel6ing us in learning the so!tware re"uired !or this 6ro?ect.

We e>6ress our sincere thanks to Mr. VENKAT NARAYANA, incharge o! CAD/CAM

laboratory !or 6roviding us the com6uter systems and the re"uired so!tware tools.

We also thank our 6arents7 class mates and !riends !or the kind su66ort given by them at all

stages o! the 6ro?ect.

1


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ABSTRACT :

The current 6ro?ect is aimed to design a low s6eci!ic s6eed centri!ugal !an.

ans belong to the !amily o! turbo machines and they move air or gas continuously

at desired velocity by action o! a rotor. low investigation o! the !an is 6lanned to

be carried out by using ANS+S9$@ so!tware !or di!!erent designed o!! design

6oints o! o6eration. The 6er!ormance o! the !an generated !rom the $D analysis at

the design 6oint will be com6ared with that o! the designed data assumed !or

calculation. This will also be com6ared with the best e!!iciency 6oint o! o6eration.

or the analysis7 an Auto $AD drawing and a 19D model the !an im6eller and casing

are develo6ed !or the designed !an. This is !ollowed by the generation o! *rid and

aerodynamic analysis using the available $D solver. The work is concluded by identi!ying

6ossible ones o! im6rovements in the design o! im6eller and casing and suggest suitable

modi!ications.

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Nome!"#$%re, Gree& "e$$er' #( S%)'!r*+$':

A Area

) Im6eller Width

! Absolute velocity

(P Incremental change in 6ressure

( Diameter

D Im6eller diameter

E &nergy

%ead7 blade s6an or height

m ,ass !low rate

S6eed in r6m

'h Sha6e number

- S6eci!ic s6eed

P Pressure

+ Sli6 6ower actor

R *as constant

r )adius

R ! )adius o! curvature o! vane

% #lade s6eed

W S6eci!ic work

Number o! blades

5


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GREEK LETTERS:

a Nole blade angle w.r.t. #lade s6eed u

B Ta6er angle at shroud

C Im6eller blade angle7relative7!low direction w.r.t. Negative o! blade s6eed

low coe!!icient

E &!!iciency

F Density

w Angular


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=.5 A66lications

3 DESIGN OF TE LOW SPECIFIC SPEED CENTRIFUGAL FAN 00 31

1.2 an S6eci!ications.

1.= $alculations

1.1 Auto $AD design o! the an Im6eller.

4 E5TRACTION OF COORDINATES00000000000. 36

4.2 ,ethod o! e>traction

4.= $oordinates o! the blade 6ro!ile :hub side;

4.1 $oordinates o! the blade 6ro!ile :shroud side;4.4 $oordinates o! the hub

4.5 $oordinates o! the shroud

2 CFD TEORY00000000000000000000 47

5.2 $D Theory

5.2.2 $ontinuity &"uation

5.2.= ,omentum &"uation

5.2.1 &nergy &"uation5.= Turbulence ,odules

5.=.2 -9 &6silon module

5.1 Discretiation o! governing e"uations

5.1.2 inite di!!erence method

5.1.= inite $ontrol volume method

5.1.1 inite element method

8 ANSYS 9 CF50000000000000000000.. 2

0.2 Introduction to ansys c!>0.= Ansys $!> and the Ansys workbench &nvironment0.1 $D Pre9Processing in [email protected] The ANS+S $@ Solver 0.5 Post9Processing with ANS+S $D9Post0.0 Industry solutions using ANS+S

METODOLOGY0000000000000000000. 22

3


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.2 ,odelling and $D analysis o! centri!ugal !an.

.= ,eridional data !or %ub and Shroud contour

.1 ,esh data !or 19D im6eller blades

.4 Selection o! solver 6arameters and convergence criteria

.5 #lade geometry 6lot

6 RESULTS AND DISCUSSIONS00000000000000

3.2 *eneral

3.=


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. INTRODUCTION

2.2 Introduction to Turbo machines

Turbomachines used !or the com6ression o! gases are classi!ied under radial7 a>ial or

mi>ed !low ty6es de6ending on the !low through the im6eller. In a radial or centri!ugal

machine7 the 6ressure increase due to the centri!ugal action !orms an im6ortant !actor in its

o6eration. The energy is trans!erred by dynamic means !rom the im6eller to the !luid. The

!luid because o! centri!ugal action is continuously thrown outwards making way !or !resh

!luid to be inducted in because o! the reduced local 6ressure. Another characteristic !eature

o! the centri!ugal im6eller is the angular momentum o! the !luid !lowing through the

im6eller is increased by virtue o! the im6eller outer diameter being signi!icantly larger than

the inlet diameter. In a>ial !low machines7 a large mass o! gas is set in motion by the

rotating im6eller and is made to move !orward because o! the aerodynamic action o! the

blades. A mi>ed !low machine encom6asses the 6ro6erties o! both the above ty6es.

De6ending on the 6ressure rise attained7 these machines are named as !ans and blower or com6ressors. There is however no distinct demarcation among the di!!erent ty6es. ans

handle gases in large volumes without a66reciable density variation. Pressure ratio

attainable is o! the order o! 2./5. They are invariably single stage machines.

#lowers cover 6ressure ratios !rom 2./5 to about 4. They are made either as single

stage or two or three stages. No inter cooling is re"uired.

$om6ressors include 6ressure ratios !rom 1 to 2= or higher. They are invariably

multistage with or without intercooling. or higher 6ressure ratios a66reciable com6ression

takes 6lace !ollowed by a reduction in volume. The calculations are done on the basis o!

mass !low in such cases.

The selection o! a ty6e o! im6eller namely a>ial7 radial or mi>ed !low !or a s6eci!ied

6ressure rise7 s6eed and !low rate !ollows !rom sha6e number considerations de!ined by

Nsha6e K n L:v;M w/.5

2/


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The sha6e number is im6ortant to achieve an o6timum e!!iciency. )adial machines

have low sha6e numbers ranging !rom /./11 to /.2= and are known as slow running

im6ellers. A>ial !low ty6es have sha6e numbers !rom /.11 to 2.5. ,i>ed !low ty6es have

values in between those o! radial and a>ial im6ellers.. An idea o! the sha6e o! im6eller can be obtained !rom the sha6e number. or e>am6le7 slow running im6ellers have long and

narrow vane channel 6assages and large shroud diameters. This increases the !riction losses

and lowers the e!!iciency7 high sha6e numbers are desirable.

The energy which is converted into 6ressure in the im6eller is indicated by the degree

o! reaction which is the ratio o! s6eci!ic 6ressure energy to the s6eci!ic work o! the machine.

#lowers and com6ressors o6erate with degree o! reaction greater than ero7 and mostly than

/.5. The reason is that the static 6ressure can be generated more e!!iciently in the im6eller

than in the guide vanes as the centri!ugal !orces in the rotating channels o! the im6eller hel6

in the suction o! the boundary layer and dead ones.

I! the s6eci!ied 6ressure rise cannot be obtained in one stage7 two or more stages as

re"uired are built in series7 the individual stages being ?oined by what are known as return

guide 6assages or return channels. In such a multistage centri!ugal com6ressor or blower7

the chie! 6roblems encountered are regarding the design o! e!!icient guide and returnchannel 6assages as well as care!ully designed shroud and vane contours. Though

com6ressors with more than eight or ten stages are in e>istence7 the number o! stages is

generally restricted to two or three. The desired 6ressure rise is obtained by em6loying high

rotational s6eeds made 6ossible by the steam and gas turbine drives and using high strength

!orged im6ellers with straight radial blades and devoid o! !ront shroud in order to minimie

the stresses in the hub and back shroud.

In blowers and !ans dealing with large volumes o! gas but relatively low 6ressure rise7

sheet metal construction is em6loyed7 with suitable hub design to take care o! stresses and

guide the !low. The sheets are suitably 6ressed to sha6e and the ?oining is through riveting

or welding.

#lade loading7 shroud or disc stresses and critical s6eed considerations im6ose serious

restrictions on the dimensions o! the machine to lower values. %owever7 s the 6ressure rise

increases with increasing 6eri6heral s6eeds7 minimum number o! stages is 6re!erred !or a

com6act blower7 thus necessitating the use o! high 6eri6heral s6eeds limited by the strength

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o! the material.

.7 FAN :

A !an can be de!ined as a volumetric machine7 which7 like a 6um67 moves a

"uantity o! air or gas !rom one 6lace to another. In doing this7 it overcomes

resistance to !low by su66lying the !luid with the energy necessary !or continued

motion. Physically essential elements o! a !an are a bladed im6eller :rotor; and a

housing to collect the incoming air or gas and direct its !low. ans7 #lowers or

$om6ressors all move air7 but at di!!erent 6ressures. At any 6oint in the !low o! air

through the im6eller7 a 6ressure head obtains the centri6etal acceleration7 so thatthe static 6ressure o! the air increases !rom the eye to the ti6 o! the im6eller.

I

.3 CLASSIFICATION OF FANS

De6ending u6on the nature o! the !low through the im6eller blades7 !ans can be

categoried as a>ial7 centri!ugal7 mi>ed or cross !low ty6e.

The ma?or categories can be !urther categoried as given belowO

Ce$r* ial ty6e

c. $ontra rotating

d. *uide9vane ty6e

e. A>ial ty6e

M*?e(


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). S9$asing

!. U9$asing

The above said !ans have di!!erent characteristics suitable !or s6eci!ic a66lications. I! the

re"uirement is to blow air in large volume rate ca6acity7 but relatively low96ressure gain7a>ial !low !ans may be suited by contrast a !an re"uired to blow air through !iltrate system

o!!ering a high !low resistance will have a relatively small volume !low rate ca6acity with

high 6ressure rise.

CENTRIFUGAL FLOW FANS

Air or gas enters the im6eller o! the !an a>ially through the suction chamber. This gas

!lows through the !low 6assage between the im6eller blades while im6eller rotates. The

action o! the im6eller swings the gas !rom a smaller radius to a larger radius and delivers the

gas at a high 6ressure and velocity to the casing. Due to im6eller rotation centri!ugal !orce

also contributes to the stage 6ressure rise. At the e>it o! the im6eller a s6iral sha6ed casing

known as scroll or volute collects the !low !rom im6eller which can !urther increase thestatic 6ressure o! air.

For>#r( C%r@e( Ce$r*ial !ans !or some duties. Its e!!iciency is less than a>ial !ans .

R#(*#" D*'!h#r=e Ce$r*


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de6ends on the whirl com6onents :$u2

7 $u=

; o! the absolute velocity vectors $2 and $

=

res6ectively. These im6ellers are em6loyed !or lower 6ressure and lower !low rates.

A5IAL FLOW FANS

The ma?or categories o! the a>ial !low !ans are sub9categoried into !our ty6esO

Pro6eller ans7 Tube9A>ial ans7 $ontra )otating ans and *uide9ial ans. ,ost

a>ial !ans are available with many blade angle settings that in some cases may be ad?usted

when stationary7 by slackening a clam6ing mechanism in the im6eller hub. The variable

6itch !acility is an advantage in so6histicated !ans that can alter the im6eller blade angle

while the !an is in o6eration. The !low coe!!icient o! the !an is 6redominantly a!!ected by the

changing o! blade angles. ans o6timied to 6roduce high !low coe!!icients are set with

large blade angles.

MI5ED FLOW FANS

The characteristics o! the mi>ed !low !ans are di!!erent !rom those o! a>ial !low !ans

and those o! centri!ugal !ans. These !ans are !re"uently used when characteristics

a66ro>imating those o! backward curved centri!ugal !ans are re"uired but the installationdictates an a>ial inlet and outlet con!iguration. (ne most common ty6e is a>ial casing

mi>ed9!low !an.

CROSSFLOW FANS

In this ty6e o! !ans the air enters the im6eller through 6eri6heral segment other than

through hub. These !ans are used where convenience is more im6ortant than e!!iciency.

These !ans are suitable !or low96ressure rise a66lications. The a66lications o! cross !low

!ans are domestic !an assisted heaters7 handhold hair dryers and air curtain.

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7. LITERATURE SURVEY

7. S+e!*or& #( S$#$*! +re''%re r*'e

In any centri!ugal machine7 the most im6ortant re"uirement is that it should

develo6 the re"uired s6eci!ic work with the desired static 6ressure rise. In other

words the s6eci!ic 6ressure rise is directly de6endent on the s6eci!ic work

develo6ed by the machine.

The s6eci!ic work is develo6ed in the im6eller only through the energy trans!er to the

!luid through the vanes and is given by &ulerRs e"uation

W K U=$= H U2$2

WK s6eci!ic work develo6ed by the stage :N.mM-g;

U2 K im6eller s6eed at start o! vane

U= K im6eller ti6 6eri6heral s6eed

$2 and $= are the com6onents the absolute velocity in the tangential direction at 6oints ?ust

be!ore the inlet to the im6eller vane and the e>it !rom the im6eller vane res6ectively.

The above &"uation can be rewritten asO

W K :U== H U2= $2=9$==W/=9W1=;M=

As the !low energy o! the !luid com6rises the 6ressure energy7 the kinetic energy and that due to

the geodetic head7 the energy at any section o! the 6assage :e>ce6t where energy is being

added; can be written asO

& K PMF $=M g.h

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7.7 BLADE ANGLES:

I"e$ @#e #="e

As the tem6erature o! the air at the inlet is less. The sonic velocity is also less.

There is the danger o! the velocity in this region reaching a sonic value .or

incom6ressible !low7 the relative inlet velocity is a minimum when C2 K15. In

com6ressible !low7 the relative inlet ,ach number is a minimum when C is in

between =5 to 1/.

E?*$ @#e #="e

There are three considerations !or C=b namely !orward curved blades i! C=bV/7 radial

blades when C=bK/ and backward curved blades i! the angle C=b/. In all the three casesC2b7 the !an s6eed7 the inlet velocity cm and sie are ke6t the same. There!ore the velocity

triangles at 2 are the same !or three cases. The velocity triangles at = are shown in the

!igures !or each case. It can be seen c=u increases with C=b and likewise the s6eci!ic work. As

C=b increases7 the blades are more cambered !inally resulting in the highly cambered

im6ulse 6ro!ile this means increase in the # =b results in increase in $=u7 likewise the

s6eci!ic work. The kinetic energy o! the !luid at the im6eller outlet becomes a smaller

6ercentage o! the total energy as blades become more backwardly curved. There!ore7 a

larger 6ortion o! the static 6ressure can be recovered in the im6eller with backward curved

vanes.

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I* O =.2 &!!ect o! &>it it increases. rom strength considerations7 trailing edge thickness cannot be

reduced to small values. Also this causes !ormation o! eddied behind the blade trailing edge and

results in wider wakes and more losses values between 25 to 15 are used.

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7.3VELOCITY TRIANGLES:

The three velocities that make a velocity triangle are namely

i #lade s6eed U

ii Absolute velocity $

iii )elative velocity W

*enerally the blade s6eed is taken as the base o! the triangle7 the direction o! U2 and U= !ollow the

direction o! rotation o! im6eller and W and $Rs direction vary de6ending on that and such that

WK$9U :In vectorial notation; is satis!ied

FIG 7.7 : Ve"o!*$ Tr*#="e #$ I"e$ o< Im+e""er

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FIG 7.3: Ve"o!*$ Tr*#="e #$ o%$"e$ o< Im+e""er

In a radial machine U= greater than U2.

Angle between $ Rabsolute velocityR and Rrelative velocityR U is X and C is the angle between W

and HU.

The !low velocities are resolved into two com6onents with res6ect to U7 the com6onent along

U is $u Ymay be $2u or $=uZ and 6er6endicular to U i.e. along meridional 6lane is $m and

similarly Wu and Wm are obtained.

To get the volume !low rate at the 6articular section $ m can be multi6lied by !low area at that

section hence its is called the R!low velocityR.

I! the 6re whirl is / then $2u K /7 hence it is desirable to design with consideration $ 2m K $=m

whenever 6ossible which also hel6s to maintain the blade angle within considerable range.

=.4 Im6eller

2


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The im6eller !orms the ma?or com6onent in the whole machine where the actual

energy trans!er to the !luid takes 6lace. In an actual im6eller7 com6lete guidance

to the !luid cannot be e>6ected due to the limited number o! vanes. The vane

thickness7 the viscous e!!ects7 the relative circulation7 return !lows and the e!!ect

due to bends make the velocity and 6ressure distribution !ar !rom uni!orm. Theactual !low de!lection is less than that obtained when the !low truly !ollows the

vanes. The di!!erence between the vane angle and the actual !low angle is

accounted by the introduction o! a !actor called sli6 !actor.

=.4.2 Sli6 In the case o! vane congruent !low7 the s6eci!ic work o! the machine is given by

WG

K U=

$=U 9

U2

$IU

The 6eri6heral com6onents o! velocity ?ust outside the im6eller are di!!erent !rom those

?ust within. This di!!erence in s6eci!ic work is due to the sli6 in the im6eller that is the !low

does not wholly !ollow the im6eller vanes. The energy trans!er obtained in 6ractice is less

than that calculated assuming the !low is one 9 dimensional and that the !luid outlet angle

e"uals the im6eller vane angle due to the relative eddy and nonuni!orm velocity 6ro!ile at

the im6eller.

P!leiderer de!ined the sli6 6ower !actor 6 given O

W blG K :62;W G

Stodola assumed that the sli6 is due to the relative eddy and that the sli6 velocity is

given byO

[ K 2 H: :\M;:Sin C= M:29]= $ot C= ;;

=/


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=.4.= Inlet


22/93

=.4.4 Im6eller outlet angle

The vane outlet angle has a ma?or e!!ect in the design and 6er!ormance o! the

im6eller. The o6timum inlet angle having been !i>ed9 by sonic velocity criterion in

the case o! a blower7 the outlet angle directly controls the sie7 6er!ormance aswell as the s6eci!ic world develo6ed The com6onent $= u increases with increasing

C= . or a given s6eci!ic work7 the 6eri6heral s6eed will come down or i! the

rotating s6eed is also !i>ed7 the diameter comes down. #ut an increase in C= could

cause adverse e!!ects at the vane boundary.

=.4.5 Im6eller outlet diameter

The im6eller outlet diameter as a ratio o! the inner diameter should not be too

large as otherwise the vane channels become long and narrow increasing the !riction

losses. (n the other hand7 a smaller ratio makes the length o! the !low traverse

inside the im6eller "uite small ham6ering the energy trans!er between the im6eller

vanes and the !luid !or radial machines the o6timum value o! this ratio is about =.

=.4.0 &!!ect o! viscosity

The viscosity o! the !lowing medium causes the boundary layer to develo6 along

the shroud and the vane !aces in the channel resulting in a decrease o! the area

available !or the !low o! the !luid.

Also 6ressure losses result because o! this. &ven sim6le !riction losses are a66reciable because o! the high relative velocities and the large amount o! wetted !low sur!ace.

#oundary layer e!!ects may be a66reciable because o! the adverse velocity

gradients o! considerable magnitude 6resent along the channel walls. When the

boundary layer is not in e"uilibrium with the 6ressure gradient across the channel7 a

!low normal to the through !low may arise which will alter the desired 6otential

!low 6attern and cause direct losses as a result o! the 6artial dissi6ation o! the

energy absorbed !rom the through !low to create the secondary motion.

==


23/93

=.4. Inlet 6assage

The inlet 6assage is meant to slowly accelerate the !luid !rom the entrance to

the eye with minimum losses. An inlet nole is usually !itted at the entrance o! the

inlet nole design is im6ortant as otherwise it may a!!ect the !low conditions at the

entrance to the im6eller.

=.4.3 &!!ect o! Sur!ace roughness

The e!!ect o! the sur!ace roughness becomes a66reciable in small im6ellers

where vane channels are very narrow. condition that is

$u. r K constant

Another ty6e o! casing normally em6loyed is the constant velocity volute

having a constant average velocity at all sections and the volute area increases in

6ro6ortion to the angular dis6lacement !rom the tor"ue where the velocity is ero.

=1


24/93

7.2 EFFECT OF GEOMETRIC AND FLOW PARAMETERS ON

FAN PERFORMANCE

=.5.2 Sie o! im6ellerO

The !low rate de6ends on im6eller diameter and the width. or 6articular stage 6ressure rise the

6eri6heral s6eed and geometry o! the im6eller can be decided. The diameter ratio :d2Md=; o!

the im6eller determines the length o! the blade 6assage. Smaller the ratio7 larger is the blade

6assage.

With slight acceleration o! the !low !rom the im6eller eye to the blade entry the !ollowing

relation !or the blade width to diameter ratio is recommended.

b2Md= K /.=

Im6ellers with backward swe6t blades are narrower i.e. b2Md=V/.=

d2 M d= K 2.=:;2M1

d2 9 Im6eller inlet diameter

d= 9 Im6eller outlet diameter

9 low coe!!icient

=4


25/93

FIG : . E


26/93


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7.8 LOSSES IN CENTRIFUGAL FANS

'osses occur in both the stationary as well as moving 6arts o! the centri!ugal !an stage. #y

accounting !or the stage losses7 the actual 6er!ormance o! a !an or blower can be 6redicted.

The various losses are given belowO

=.0.2 'osses in Im6eller

The losses are categoried here as

a; Im6eller internal losses and

b; Im6eller e>ternal losses

Im6eller Internal 'osses

The im6eller internal losses are those due to skin !riction7 blade loading7 and blade9wake

mi>ing and im6eller shroud clearance. Im6eller skin9!riction loss is de!ined as the loss

e>6erienced by the !luid while !lowing through the channels !ormed by the bounding

sur!ace o! the im6eller. These losses s6eci!ically e>clude the e!!ects o! the non uni!orm

velocity distribution caused by the work9addition 6rocess in the im6eller on the blade9

sur!ace boundary9layer behavior.

Im6eller &>ternal 'osses

The im6eller e>ternal losses are those due to disk !riction7 recirculation at the im6eller edges7

and leakage around shrouded im6ellers. The disk9!riction loss is that due to the shear !orce

acting on the im6eller caused by the !luid between the rotating and stationary sur!aces. The

recirculation and scrubbing loss is that due to internal recirculation at either im6eller9shroud

clearance or at the im6eller e>it7 where in the !luid loses momentum in the 6rocess o!

!lowing back to the im6eller and there!ore necessitates an increase in the amount o! work

re"uired to be su66lied by the im6eller.

=


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=.0.= 'eakage 'osses

A clearance is 6rovided between the rotating 6eri6hery o! the im6eller and the casing at

the entry. This leads to the leakage o! some air and disturbance in the main !low !ield.

#esides this7 leakage also occurs through the clearance between the !an sha!t and the casing.

=.0.1 Di!!user and 6ands to a large cross sectional area in the volute. This leads to losses due to eddy

!ormation .urther losses occur due to the volute 6assage !riction and !low se6aration.

7. FAN APPLICATIONS

Some o! the im6ortant a66lications are Steam Power stations7 iliaries

In Steam Power 6lants !orced dra!t and induced dra!t !ans are used to raise the 6ressure o!

air and !lue gases to overcome the draught losses in the !low 6assage o! steam boiler. The

!orced dra!t !an raises the 6ressure o! the ambient air and delivers it to the boiler !urnace

through air 6re9heater. The induced dra!t !an is located between the !urnace and the !lue gas

chimney. There!ore these !ans work in the hostile atmos6here o! high tem6erature :25/degrees to 15/ degrees centigrade; abrasive and corrosive gases. These !ans are either a>ial

or centri!ugal ty6e and generally driven by electric motors. or 6ulveriing coal or !uel oil

small and large !ans are used.

$ooling o! ,otors7 *enerators and &ngines

In internal combustion engines and electric motors and generators considerable e>tent o! heat is needed to be removed. The cooling o! the hot water in the radiators o! an automobile

=3


29/93

vehicle is a well9known e>am6le. The air sucked through the radiators cools the circulating

water as well as the engine. or this 6ro6eller !ans are used and driven by the engine

through belt transmission drive. or cooling the electric motors7 !ans are generally mounted

on the e>tension o! their sha!ts.

Air $irculation and ,ine


30/93

3.DESIGN OF TE LOW SPECIFIC SPEED

CENTRIFUGAL FAN

3. F# S+e!*


31/93

The value is !ound out to be K 5.50=

Im6eller ti6 diameter :D=; K :M2.305=;^:L :`;M%.=5; Yselected value is 2.11 mZ

Im6eller ti6 s6eed :U=; K 03.=4 mMs

&ntrance coe!!icient K $2mML :=W;K/.=5 :assuming K/.=H/.1 !or blowers and !ans;

There!ore meridional velocity at inlet $2m K 2.4 mMs

Also $=m K 2.4 Yassumed that 6re whirl is eroZ

$/ K 20.12 mMs :$2mM $/ K2.2;

&ye diameter K 4 ^L ::` M c/;M \; K /.5// m

Im6eller Inlet diameter D2 K /.55/ m : DeMD2K2.2;

12


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$orres6onding A2 :` M $2m; K /.233m=

Width b2 K :A2 M D2; K/.2/15m

Ti6 in let s6eed U2 K \ D2 N M0/ K =3.== mMs

rom velocity triangles Tan C2 K $2mMU2 K/.015

C2 K 1=.44


33/93

tan C=b K 1.14 :tan C=b Kc=mM:U=9$=ublG;;

=b K 1.1 YC=b selected K 1./Z

F*r'$ Tr*#" :

K 2=. Y K k :r =r 2;M:r =9r 2;^sin:C2bC=b;M=Z

selected K 21

A=MA2 mean K 2.2

A=K /.1/50

b= K /./1 Yb= :selected; K /./1Z


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PK /.=03 YPK =^fRM^:2M:29:r 2Mr =;=;Z

2 M :2P; K /.33

W blG K 4/12 :w blMsig96!l;

$=ublG K 5./0 :w blGMU=;

tan C=b K 2.253=Yc=mbM:u=9c=ublG;Z

=b K 4.=

=b :selected; K 5/

Th*r( Tr*#":

K 2/.1 Y selected K 2/Z


35/93

3.3 AUTO CAD DESIGN OF TE FAN IMPELLER:

$om6uter9aided design :$AD; is the use o! com6uter technology !or the design o!

ob?ects7 real or virtual. $AD o!ten involves more than ?ust sha6es. As in the manual dra!ting

o! technical and engineering drawings7 the out6ut o! $AD o!ten must convey also symbolic

in!ormation such as materials7 6rocesses7 dimensions7 and tolerances7 according to

a66lication9s6eci!ic conventions.

$AD may be used to design curves and !igures in two9dimensional s6ace_ or curves7

sur!aces7 and solids in three9dimensional ob?ects. It is an im6ortant industrial art e>tensively

used in many a66lications7 including automotive7 shi6building7 and aeros6ace industries7

industrial and architectural design7 6rosthetics7 and many more. $AD is also widely used to

6roduce com6uter animation !or s6ecial e!!ects in movies7 advertising and technical

manuals.

$AD has become an es6ecially im6ortant technology within the sco6e o! com6uter9aided

technologies7 with bene!its such as lower 6roduct develo6ment costs and a greatly shortened

design cycle. $AD enables designers to lay out and develo6 work on screen7 6rint it out and

save it !or !uture editing7 saving time on their drawings.

Auto$AD so!tware is used to design a two9dimensional model o! the im6eller !an and it

is also used in e>traction o! co9ordinates. The 6rocess is e>6lained in detailed ste6s with the

assist o! !igures below

15


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ig 4.2 an Auto $AD design 2.

2; Taking intersection o! a>es as the centre and radius draw = circles o! radius =5 mm and 005 mm.

These !orm the inner diameter and outer diameter o! the im6eller. :igure 2;

=; Draw another circle taking radius as 33 mm7 and then draw o! radius 2/=3mm and centre as the

intersection 6oint o! the > a>is and the inner diameter. :igure 2;1; Two intersection 6oints are obtained on either side o! the horiontal a>es. De6ending on the direction

o! the blades one o! the 6oints is chosen. Since we went !or clockwise direction we choose the le!t

hand side 6oint. :igure 2;

4; rom this 6oint another circle o! radius r c K 2/=3mm is drawn. :igure =;

5; This circle 6asses through the inner and outer diameter circles and the arc contained by these two

circles !orms the blade. :igure =;

ig 4.= an Auto $AD design = ig 4.1 an Auto $AD design 1

0; The enclosed arc is the median o! the blade and it is shown in !igure 1.; Taking =mm o!! set on either side o! the blade median curve7 two identical curves are drawn. The to6

curve is the 6ressure side and the bottom curve is the suction side. :igure 4;

10


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ig 4.4 an Auto $AD design 4

3; A!ter obtaining one blade mirroring is used7 where the numbers o! blades are s6eci!ied as 2/ andangle as 10/.

; To generate the side view the ta6er is considered and the !ollowing !igure is generated

1


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4. E5TRACTION OF COORDINATES

4. Me$ho( o< E?$r#!$*o

The coordinates o! blade7 hub and shroud are e>tracted !rom the =9d diagram o! !an im6eller.

$oordinates are used in generating a 1D !igure in turbo grid.

A series o! coordinates are absorbed !rom a =D cad diagram7

i. The $AD diagram is !irst sim6li!ied to re6resent one blade 6assing through one o! the a>is.

ii. urther more the area between the inner radius and outer radius are divided at a series o!

e"ual intervals.

iii. or e>am6le a series o! concentric circles are drawn considering the center o! the im6eller as

shown in the !ig.

iv. These lines intersect the blade 6ro!ile at both 6ressure and suction side and also intersecting

the a>is as shown.

v. $onsidering the geometrical > a>is as y a>is an geometrical y a>is as > a>is7 using the crock

screw thumb rule the meridional geometrical > a>is re6resents a>is.

vi. Now7 considering the intersection 6oint on the blade 6ro!ile the 6er6endicular distance !rom> and y as shown in !ig.7 the > and y coordinates are absorbed.

vii. or the similar 6oint the circle 6assing through the intersection also 6asses through the

geometrical @ a>is as seen in !ig.7 a 6er6endicular is drawn to the meridional diagram.

viii. rom the meridional diagram7 as de!ined earlier the geometrical > a>is is the a>is7 !rom

this the 6er6endicular intersection the meridional diagram at both hub and shroud the 9

hub and 9shroud coordinates are e>tracted7 as the re6resentation uses the crock screw

thumb rule the values o! is considered negative.i>. And !or the leading edge a series o! concentric circles with a di!!erence o! =mm are drawn

and coordinates are generated !or the >7 y7 9hub7 9shroud.

>. As the value o! is generated !or both hub and shroud7 by varying the values o! 7

6ro!ile.curve coordinates are generated as a set !or hub using the 9hub coordinates7 and a

set !or the 9shroud.

13


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4.= $(()DINAT&S ( T%& #'AD& P)(I'& :%U# SID&;

R 5 Y

=5 =5 / /=5. =5.3 9/.2304 /

=0.03 =0.03 / /

=.0533 =.052 /.23 /

1/5 1//.=54 51.402 /

145 1=1.0511 22./3/ /

135 142./01 23.0/0 /

4=5 151.23 =15.=1 /

405 101.=14 =/.123 /

5/5 10.41 144.1/53 /

545 1=.10 1.0/4 /

535 11.2/35 45/.4==3 /

0=5 12.2543 5/=.30/ /

005 100.120 554.4 /

005 10=.//= 55.314= /

0=5 100.102 5/5.45 /

535 10.=123 451.54= /

545 103.352 4/2.=/32 /

5/5 105.5=1 143.=2 /

405 15.02/0 =4.5= /4=5 15/.51 =1.35= /

135 113.=03 231.3454 /

145 1=2.103 2=5.2=5 /

1/5 =3.34= 0/.3=22 /

=.0533 =.412 2/.2544 /

=0.03 =0.5034 3.2033 /

=5. =5.3==5 0.54// /

=5 =5 / /

1


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4.1$(()DINAT&S ( T%& #'AD& P)(I'&: S%)(UD SID&;

R 5 Y

=5 =5 / 2/4.///

=5. =5.3 9/.2304 2/1.35

=0.03 =0.03 / 2/1.10

=.0533 =.052 /.23 2/1.534

1/5 1//.=54 51.402 .1/3

145 1=1.0511 22./3/ 1./52

135 142./01 23.0/0 30.5

4=5 151.23 =15.=1 3/.513

405 101.=14 =/.123 4.=3=

5/5 10.41 144.1/53 03./=0

545 1=.10 1.0/4 02.0

535 11.2/35 45/.4==3 55.521

0=5 12.2543 5/=.30/ 4.=50

005 100.120 554.4 41.///

005 10=.//= 55.314= 41.///

0=5 100.102 5/5.45 4.=50

535 10.=123 451.54= 55.521

545 103.352 4/2.=/32 02.0

5/5 105.5=1 143.=2 03./=0

405 15.02/0 =4.5= 4.=3=

4=5 15/.51 =1.35= 3/.513

135 113.=03 231.3454 30.5

145 1=2.103 2=5.2=5 1./52

1/5 =3.34= 0/.3=22 .1/3

=.0533 =.412 2/.2544 2/1.534

=0.03 =0.5034 3.2033 2/1.10

=5. =5.3==5 0.54// 2/1.35

=5 =5 / 2/4.///

4/


41/93

4.4 $(()DINAT&S ( %U# $U)


42/93

2. CFD TEORY

2. CFD TEORY:

$D is 6laying a strong role as a design tool as well research tool. In $D7 the !undamental

e"uations o! !luid mechanics are based on the !ollowing universal laws o! conservationO

2. $onservation o! mass

=. $onservation o! momentum

1. $onservation o! energy.

2.. Co$*%*$ E-%#$*o:

Physical 6rinci6leO ,ass is conserved.

Net mass !low out Time rate o! o! control volume K decrease o! mass

through sur!ace S inside control volumePartial di!!erential e"uation !orm o! the continuity e"uation in di!!erentiable conservative !orm

can be e>6ressed as

4=

undamental 6hysical 6rinci6les *overning e"uations o! !luid !low

,ass is conserved $ontinuity e"uation

NewtonQs second law ,omentum e"uation

&nergy e"uation

&nergy conserved


43/93

Where7 Density

>7 y7 $artesian $oordinates

u7 v7 w velocity vectors in >7 y7 directions.

'.%.S Net mass !low out o! the control 6assing out o! the control sur!ace7

which surrounds the control volume. This e"uation is based on &ulerian a66roach. In thisa66roach7 a !i>ed control volume is de!ined and the changes in the !luid are recorded as the

!luid 6asses through the control volume. In the alternative 'agrangian a66roach7 an observer

moving with the !luid element records the changes in the 6ro6erties o! the !luid element.

&ulerian a66roach is more commonly used in !luid mechanics. or a $artesian coordinate

system7 where u7 v7 w re6resent the >7 y7 com6onents o! the velocity vector7 the continuity

e"uation becomes

M t M > : u; M y : v; M : w; K/

2..7 Mome$%m E-%#$*oO

%ere7 Physical 6rinci6leO K ma :NewtonRs second law;

NewtonRs Second 'aw a66lied to a !luid 6assing through an in!initesimal7 small7 moving !luid

element. (nly the !orces in the > direction are considered and the momentum is conserved

in this direction and thus the @ com6onent o! the momentum e"uation is derived.

41


44/93

orces on a !luid element can be classi!ied in a tree diagram asO

#ased on the above classi!ication o! !orces the momentum e"uation in di!!erentiable

conservative !orm can be e>6ressed as

in @ direction

in + direction

in direction

44


45/93

Where7 < stands !or the velocity vector o! the !luid.

'.%.S re6resents the Substantial derivative o! the 6roduct o! mass and acceleration

).%.S re6resents the summation o! Pressure !orce7 Normal and shear !orce7 body !orce

jt re6resents rate o! increase o! momentum 6er unit volume.

<

re6resents the rate o! momentum lost by convection

through the control volume sur!ace.

f

re6resents the body !orce 6er unit volume.

2..3 Eer= E-%#$*o:

Physical 6rinci6leO &nergy is conserved.

The 6hysical 6rinci6le stated above is nothing more than the !irst law o!

thermodynamics. When a66lied to a !luid 6assing through an in!initesimal !i>ed control

volume yields the energy e"uation i.e. increase in energy in the system is e"ual to the heat

added to the system 6lus the work done on the system.

or a !luid element it can be re6resented asO

&nergy in di!!erent conservation !orm is e>6ressed asO

45


46/93

Where7

e internal energy

V^2/2 -inetic &nergy

- $oe!!icient o! thermal conductivity'.%.S the rate o! $hange o! energy inside a !luid element

irst !our terms in the ).%.S corres6onds to the Net lu> o! heat into the element

)est o! the Terms in the ).%.S corres6onds to the )ate o! Work Done on the luid &lement

Due to Sur!ace and #ody orces.

In terms o! enthal6y7 the !inal !orm o! &nergy e"uation is

φ δ

δ ρ +∇−+= q

t

Q

Dt

Dp

Dt

Dh.

Where is known as dissi6ation !unction.

2.7. T%r)%"e!e Mo(e"':

S6ecial attention needs to be 6aid to accurate modeling o! turbulence. The 6ur6ose o! a

turbulence model is to 6rovide numerical values !or the )eynolds stresses at each 6oint in

the !low. The ob?ective is to re6resent the )eynolds stresses as realistically as 6ossible7

while maintaining a low level o! com6le>ity. The turbulence model chosen should be best

suited to the 6articular !low 6roblem. A wide range o! models is available and ty6e o! model

that is chosen must be done so with care. It is understood that these models are not used

when modeling laminar !lows.

The !inal result o! the !low7 turbulence7 reaction7 heat trans!er7 and multi6hase

calculations will be a detailed ma6 o! the local li"uid velocities7 tem6eratures7 chemical

reactant concentrations7 reaction rates7 and volume !ractions o! the various 6hases. These

outcomes can be analyed in detail using gra6hical visualiation7 calculation o! overall

6arameters and integral volume or sur!ace averages7 and com6arison with e>6erimental or

6lant data. This analysis 6hase is re!erred to as 6ost 6rocessing. #ecause o! im6rovements in

40


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48/93

The most commonly used variable !or obtaining the length scale is dissi6ation rate o!

turbulent kinetic energy denoted by &. *enerally the turbulent kinetic energy is e>6ressed as

turbulent intensity σ as de!ined below.

===RRR

=M2 wuk ++= ν 7 kK :Actual -.& in !low H mean -.& in !low;

ε ρ µ

ν σ

µ M

1

2

=

=M2RRR ===

k C

wu

U

T =

++=

The trans6ort PD& used in standard k9! model are as !ollows

( ) ρε δ ρ µ µ µ ρ −∂∂

−

∂∂

+∂∂

+

∂∂

+∂∂

= j

iij

i

j

j

iT

j

k T

j x

uk

x

u

x

u

x

k

x Dt

k D

1

=Pr MM

2. 3. D*'!re$*#$*o o< Go@er*= E-%#$*o':

The above governing 6artial di!!erential e"uations are continuous !unctions o! >7 y7 . In

the !inite di!!erence a66roach7 the continuous 6roblem domain discretied7 so that the

de6endent variables are considered to e>ist only at discrete 6oints.

&"uilibrium 6roblems usually result in a system o! algebraic e"uations that must be solved

simultaneously throughout the domain in con?unction with s6eci!ied boundary values. These

are mathematically known as elli6tic 6roblems. ,arching 6roblems result in algebraic

e"uations that usually solved one at a time. These are known as 6arabolic or hy6erbolic

6roblems.

Three methods are generally used !or discretiation7

2. inite di!!erence method.

=. inite control volume method.

1. inite element method.

5.1.2 inite Di!!erence ,ethod:

In terms o! the !low9!ield variables7 6artial di!!erential e"uations are totally re6laced by a

system o! algebraic e"uations7 which can be solved !or the values o! the !low9!ield variables

43


49/93

at the discrete 6oints only. In this sense 6artial di!!erential e"uations have been discretied.

This method o! discretiation is called Finite differene !eth"d . ,ost common !inite9

di!!erence re6resentations o! derivatives are based on TaylorQs series e>6ansion.

;:727

x#

x

uu ji ji ∆+

∆

−+ orward di!!erence

ji x

u

7

∂∂

K ;:277 x# x

uu ji ji ∆+∆− − #ackward di!!erence

( :∆ >; K truncation error due to neglected terms in series.

These are called !irst9order di!!erence e"uations. So the 6artial di!!erence e"uations have

re6laced by !inite di!!erence re6resentation 8 !inally converted into algebraic e"uations. It

is 6erha6s the sim6lest method to a66ly on uni!orm meshes7 but it re"uires a high degree o!

regularity o! the mesh. This scheme was once 6o6ular.

5.1.= inite ed region in s6ace known as

control volumep. This integral !orm o! the conservation statement is usually well known

!rom !irst 6rinci6les7 or it can in most cases7 be develo6ed !rom the PD& !orm o! the

conservation law.

$onsider unsteady =9D heat conduction. The a66ro6riate !orm o! the conservation statement

!or the control volume can be re6resented mathematically7

/. =+∂∂ ∫∫ ∫∫∫ nd$qd%t T

& % ρ

The !irst term in the above e"uation is an integral over the control volume7 re6resents the time

rate o! increase in the energy stored in the volume. The second term7 an integral over the

sur!ace o! the volume7 re6resents the net rate at which energy is conducted out through the

sur!ace o! the volume. This is the integral or control9volume !orm o! conservation law. The

integral a66roach includes the inite volume method and inite element method. The


50/93

Also since the integral e"uations are solved directly in the 6hysical domain7 no co9ordinate

trans!ormations re"uired. Another advantage o!


51/93

a66lied to solve wide9ranging !luid !low 6roblems !or over =/ years. At the heart o! ANS+S

$@ is its advanced solver technology7 the key to achieving reliable and accurate solutions

"uickly and robustly. The modern7 highly 6arallelied solver is the !oundation !or an

abundant choice o! 6hysical models to ca6ture virtually any ty6e o! 6henomena related to

!luid !lowO laminar to turbulent :including transition;7 incom6ressible to !ully com6ressible7subsonic to trans9 and su6ersonic7 isothermal or with heat trans!er by convection andMor

radiation7 non9reacting to combusting7 stationary andMor rotating devices7 single !luids and

mi>tures o! !luids in one or more 6hases :incl. !ree sur!aces;7 and much7 much more. The

solver and its many 6hysical models are wra66ed in a modern7 intuitive7 and !le>ible *UI

and user environment7 with e>tensive ca6abilities !or customiation and automation using

session !iles7 scri6ting7 and a 6ower!ul e>6ression language.

0.= ANS+S $@ and the ANS+S Workbench &nvironment

ANS+S $@ so!tware is !ully integrated into the ANS+S Workbench environment7 the

!ramework !or the !ull suite o! engineering simulation solutions !rom ANS+S. Its ada6tive

architecture enables users to easily set u6 anything !rom standard !luid !low analyses to

com6le> interacting systems with sim6le drag9and9dro6 o6erations. Users can easily assess

6er!ormance at multi6le design 6oints or com6are several alternative designs. Within the

ANS+S Workbench environment7 a66lications !rom multi6le simulation disci6lines can

access tools common to all7 such as geometry and meshing tools.

Geome$r: ANS+S Design,odeler so!tware is s6eci!ically designed !or the creation and

6re6aration o! geometry !or simulation. Its easy9to9use7 !ully 6arametric environment with

direct7 bidirectional links to all leading $AD 6ackages acts as the geometry 6ortal !or all

ANS+S 6roducts to 6rovide a consistent geometry source !or all engineering simulations.

Me'h*=: Providing accurate $D results re"uires su6erior meshing technology. ANS+S,eshing 6rovides a multitude o! meshing technologies in a single a66lication to allow users

to select the best o6tion on a 6art9by96art basis. ANS+S I$&, $D meshing tools also are

available and include unlimited mesh editing ca6abilities as well as structured he>ahedral

meshing.

0.1 $D Pre9Processing in $@9Pre

The ANS+S $@ 6hysics 6re96rocessor is a modern and intuitive inter!ace !or the setu6

52


52/93

o! $D analyses. In addition to a general mode o! o6eration7 6rede!ined wiards are

available to guide users through the setu6 o! common !luid !low simulations. A 6ower!ul

e>6ression language gives users the ability to customie their 6roblem de!inition in

numerous ways7 such as with com6le> boundary conditions7 6ro6rietary material models or

additional trans6ort e"uations. The ada6tive architecture o! $@9Pre even allows users tocreate their own custom *UI 6anels to standardie in6ut !or selected a66lications7 and

thereby ensure adherence to established best 6ractices.

0.4 The ANS+S $@ Solver

At the heart o! ANS+S $@ so!tware is its advanced solver technology using cou6ledalgebraic multigrid7 the key to achieving reliable and accurate solutions "uickly and

robustly. Its engineered scalability ensures a linear increase in $PU time with 6roblem sie

and 6arallel 6er!ormance that is second to none. Users can !ollow convergence 6rogress and

dynamically monitor numerical and 6hysical solution "uantities. Solver 6arameters7

boundary conditions and other 6arameters can be ad?usted on the !lyQ7 without sto66ing the

solver. The ANS+S $@ solver uses second order numerics by de!ault7 ensuring users

always get the most accurate 6redictions 6ossible. All simulations7 whether !or rotating

machinery7 multi6hase !lows7 combustion or any other 6hysical model bene!it enormously

!rom the cou6led solver technology in ANS+S $@ so!tware to achieve robust and scalable

!low solutions.

0.5 Post9Processing with ANS+S $D9Post

$om6lete and 6ower!ul 6ost96rocessing ca6abilities !or ANS+S $@ results are 6rovided

with ANS+S $D9Post !or both gra6hical and "uantitative analysis. Together with !ull

scri6ting and automation7 including re6ort generation7 $D9Post ensures users get the most

out o! their $D simulations.

0.0 Industry solutions using $@

5=


53/93

. Vor$e? '$r%!$%re' * #


54/93

4. Pre(*!$*o o< >e$e'' (*'+er'*o %(er oe-%*"*)r*%m !o(*$*o'


55/93

.Mo(e""*= #( CFD A#"'*' o< Ce$r* Dom#*:

#e!ore constructing grid7 it is re"uired to understand the e>act !low domain 6ro6erly. The

!low domain in the case o! $entri!ugal !an consists o! Im6eller7 where Im6eller is a rotating

com6onent and others are stationary. It is there!ore re"uired that be!ore going ahead with 1D

modelling and grid generation7 the common inter!aces should be clearly de!ined. The

so!tware that is used is decided later based on nature and com6le>ity o! the geometry. or

a>is9symmetry bladed geometry7 the data !or hub7 shroud and blade 6ro!iles are obtained

!rom =D drawing and subse"uently grids are generated using Turbo9*rid so!tware..

The boundary wall is the region where no sli6 condition e>ists and the velocity gradually

increases and reaches to mainstream velocities. That means7 velocity gradient e>ists there

and that region close to the boundary wall should have !ine grids.

3D CAD MODELLING:

3D Geome$r*!#" Mo(e" o< Im+e""er:

The blade o! the 6resent Im6eller is o! 1D ty6e and the modelling o! Im6eller blade is

rather com6le> com6ared to =D curved blades. 1D blade involves thickness and twist

distribution as the blade e>tends between hub and shroud sur!aces.

The geometrical design o! blade 6ro!ile is e>tracted !rom blade co9ordinates o! line

elements7 camber sur!ace and distribution o! thickness on the camber sur!ace. The basic

design data is given in the !orm >7 y7 co9ordinates o! line elements. 'ine elements arelocated along the radial 6ositions o! the blade7 and some o! the line elements are located

55


56/93

u6stream o! the blade leading edge7 and like9wise also e>tends downstream o! the trailing

edge. The sam6le data !or line elements are given in the7 this data is arranged in order to

obtain hub and shroud blade 6ro!iles. This 6rocess re"uires 6rogramming !ile in

TU)#(*)ID7 which can trans!er large amount line data instantly.

CUTTING TE TRAILING AND DRIVING SURFACES

%ub.curve

5 Y

/ / 9254/ / 92553/ / 9225

2=/ / 9520/ / 915

25 / /=5 / /145 / /005 / /

Shroud.curve

5 Y

=4.04/ / 92=.00/2=5/.402 / 92=4.00/2

=5=./522 / 922.00/2=54.04 / 9224.00/2=5.04 / 92/.00/2

=2./= / 92/4.013005 / 941

.7MERIDIONAL DATA FOR UB H SROUD CONTOURS

#y using the above data we get the meridional view o! the hub and shroud contours o!

the im6eller as shownThe hub curve runs u6stream to downstream and must e>tend o! the blade leading

edge. The hub data !ile contains the hub curve data 6oints in $artesian !orm and

downstream o! the blade trailing edge. The 6ro!ile 6oints are listed7 line9by9line7 in order

!rom u6stream to downstream. These data 6oints are used to 6lace the nodes on the hub

sur!ace7 which is de!ined as the sur!ace o! revolution o! a curve ?oined by these 6oints.

Shro%( D#$# F*"e

The shroud data !ile contains the shroud curve data 6oints in $artesian or cylindrical !orm the

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shroud curve runs u6stream to downstream and must e>tend u6stream o! the blade leading

edge and downstream o! the blade trailing edge the 6oints are listed7 line by line in !ree

!ormat style in order !rom u6stream to downstream. These data 6oints are used to 6lace the

nodes on the shroud sur!ace7 which is de!ined as the sur!ace o! revolution o! a curve ?oined

by these 6oints.&>am6le: $onsidering @ Plane with Q as A>is o! )otation

igO %ub $urve and Shroud $urve Pro!ile curve Data ileO

The 6ro!ilep data !ile contains the blade 6ro!ilep curves in $artesian or cylindrical !orm.The 6ro!ile 6oints are listed7 line9by9line7 in a closed loo6 surrounding the blade. The blade

6ro!iles should lie on a sur!ace o! revolution to !acilitate trans!ormation to m96rime7 theta

con!ormal s6ace.

A minimum o! two blade 6ro!iles are re"uired7 one which lies e>actly on the hub sur!ace

and one which lies e>actly on the shroud sur!ace. The 6ro!iles must be listed in the !ile in

order !rom hub to shroud. ,ulti bladed geometries are handled by 6lacing multi6le blade

6ro!ile de!initions in the same 6ro!ile.

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Pro!ile. $urveO

Pro!ile 25 Y

=5 / /=5.3 9/.2304 /=0.03 / /=.052 /.23 /1//.=54 51.402 /1=1.0511 22./3/ /142./01 23.0/0 /151.23 =15.=1 /101.=14 =/.123 /10.41 144.1/53 /1=.10 1.0/4 /11.2/35 45/.4==3 /12.2543 5/=.30/ /

100.120 554.4 /10=.//= 55.314= /100.102 5/5.45 /10.=123 451.54= /103.352 4/2.=/32 /105.5=1 143.=2 /15.02/0 =4.5= /15/.51 =1.35= /113.=03 231.3454 /1=2.103 2=5.2=5 /=3.34= 0/.3=22 /=.412 2/.2544 /=0.5034 3.2033 /=5.3==5 0.54// /=5 / /

#Profile 2

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5 Y

=5 / 2/4.///=5.3 9/.2304 2/1.35=0.03 / 2/1.10=.052 /.23 2/1.5341//.=54 51.402 .1/3

1=1.0511 22./3/ 1./52142./01 23.0/0 30.5151.23 =15.=1 3/.513101.=14 =/.123 4.=3=10.41 144.1/53 03./=01=.10 1.0/4 02.011.2/35 45/.4==3 55.52112.2543 5/=.30/ 4.=50100.120 554.4 41.///10=.//= 55.314= 41.///100.102 5/5.45 4.=5010.=123 451.54= 55.521103.352 4/2.=/32 02.0105.5=1 143.=2 03./=015.02/0 =4.5= 4.=3=15/.51 =1.35= 3/.513113.=03 231.3454 30.51=2.103 2=5.2=5 1./52=3.34= 0/.3=22 .1/3=.412 2/.2544 2/1.534=0.5034 3.2033 2/1.10

=5.3==5 0.54// 2/1.35=5 / 2/4.///

The !irst ste6 is to check whether the blade 6ro!ile data obtained !rom solid model is

intersecting hub and shroud curves or not. We use $@9Turbogrid intersect o6tion !or this

6ur6ose. Using this o6tion7 we have to see that blade 6ro!ile must lie on the sur!ace o!

revolution o! hub and shroud as shown in !ig Turbo grid intersecting ca6ability can convert

an e>isting set o! blade 6ro!iles that does not necessarily lie on the sur!ace o! revolution into

one that can be used in a $@9Turbogrid tem6late.

Ne>t ste6 is generating grid. Among the various tem6lates available in turbogrid7 ,ulti

#lock *rid tem6late as shown in !ig is used. #y the way o! ad?usting control 6oints in !ig a

good "uality he>ahedral grid can be generated. li6 to6ology is used to correct negative grid

volume due to le!t9handed system. The mesh command creates mesh grid but also calculates

and dis6lays the minimum and ma>imum skew angle in the grid and the node at which it

occurs. The


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Setting the to6ology !or the mesh grid

Ad?usting the control 6oints at the 'eading &dge 8 Trailing &dge

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19D view o! im6eller without shroud sur!ace

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VIEWS FOR 3D IMPELLER BLADE MES

The *= +#r#me$er' >ere !o'*(ere( $o !he!& $he -%#"*$ o< $he =r*(':

S&e> #="e: It is de!ined as the internal angle o! the octahedron. Ideally7 all the

angles should be e"ual to / degrees to get a 6er!ect orthogonal grid. %owever7 !or

6ractical 6ur6oses7 the grid is considered to be o! high "uality i! the minimum

skew angle is not lower than 25 degrees and the ma>imum skew angle is not

greater than 205 degrees.

Gr*( @o"%me: Negative volume meant overla66ing o! ad?acent grids7 which would

lead to errors in solver. $are was taken to ensure that there was no negative

volume in the grids.

A'+e!$ r#$*o: It is de!ined as the ratio o! the longest side to the shortest side. Its

minimum value is 2. or good "uality grid creation7 the ma>imum as6ect ratio

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should be less than =//.

The mesh is generated !or the 1D Im6eller with the total number o! nodes7 ma>imum

and minimum skew angle and as6ect ratio obtained !rom TU)#(*)ID are given

in Table 4.1.

.3MES DATA FOR 3D IMPELLER BLADES

S.No Com+oe$ N%m)er o<

No(e'

N%m)er o A="e

3DIMPELLER ;361 8327 6 83

S+e!*tensionsO . =r(J,

.=!*J, .)!


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average o! the boundary condition tem6eratures.

In the 6re 6rocessing the !ollowing !luid domains and boundary conditions are

s6eci!ied.

2. Simulation O Steady State

=. Domains O luid

• )2 O Im6eller :)otating;

1. #oundary $onditionsO

• Inlet O Im6eller inlet

• (utlet O Im6eller e>it

• Inlet )elative Pressure O 2./21= bar

• Wall O smooth

• ,ass !low O 1.0= kgMs

4. luid Pro6ertiesO

• Working luid O air at =5$• Density O 2.= kgMm1

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5. )otation A>is O

0. Turbulence ,odelO

• Turbulence ,odel O k9&6silon• %eat trans!er ,odel O None

. Inter!aceO

• Ty6e O luid 9luid

• Inter!ace models O )otational 6eriodicity

3. Write Solver ileO

A!ter s6eci!ying all conditions write de!inition !ile using write solver !ile

command.

.4 Se"e!$*o o< 'o"@er +#r#me$er' #( !o@er=e!e !r*$er*#:

The !low governing e"uations are solved in $@9Solver. The $@9Solver ,anager is

a gra6hical user inter!ace used to set attributes !or a $D calculation7 $ontrol the $@9

Solver interactively and to


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accurate but less robust. cessive di!!usivity can occur. It is there!ore recommended to use a value o! /.5

!or good accuracy o! $D results.=. Timescale $ontrol !or a steady state simulationO The selection o! an a66ro6riate

time ste6 sie is essential in order to obtain good convergence rates !or simulation.

In general there are two situations in which we use a 6hysical time ste6O

• to 6rovide su!!icient rela>ation o! the e"uation non9linearityQs so that a

converged steady state solution is obtained7 or7

• To evolve the solution through time in order to 6rovide transient

in!ormation about a time de6endent simulation.

Ph'*!#" T*me '$e+

This o6tion allows a !i>ed time ste6 sie to be used !or the selected e"uations over the

entire !low domain. or advection9dominated !lows7 the 6hysical time ste6 sie

should be some !raction o! a length scale divided by a velocity scale. A good

a66ro>imation is the Dynamical Time !or the !low. This is the time taken !or a

6oint in the !low to make its way through the !luid domain. or many simulations areasonable estimate is easy to make based on the length o! the !luid domain and the

mean velocity7

1. ,a>. No. Iterations are the ma>imum number o! iterations the $@9Solver will

run.

4. )esidual Ty6e is set to either ),S or ,A@ and a residual target is s6eci!ied !or

the convergence. The residual is a measure o! the local imbalance o! each

conservative control volume e"uation. It is the most im6ortant measure o!

convergence as it relates directly to whether the e"uations have been solved. We

can either select ,A@ :ma>imum; or ),S :root mean s"uare; normalied values

o! the e"uation residuals as your check !or convergence. The $@9Solver will

terminate the run when the e"uation residuals calculated using the method

s6eci!ied is below the )esidual Target value.

or the 6resent simulation Solver Parameters are s6eci!ied as !ollowsO

• Advection scheme OS6eci!ied #lend actor :/.5;

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• Time Scale $ontrol OPhysical Time Scale :/.///1 sec;

• ,a>imum Iterations O =//

• )esidual $onvergence criteria O ),S

• )esidual $onvergence TargetO 2&91

5. )un the solver monitor.

The solver is allowed to run till the re"uired convergence is obtained.

.2 B"#(e Geome$r P"o$

Isometric 19D view o! blade7 hub 8 shroud

03


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,eridional view

B"#(e me'h +"o$

,esh element at 5/ s6an

POST PROCESSING:

$@9Post is a !le>ible state9o!9the9art 6ost96rocessor. It is designed to allow easy

visualiation "ualitative and "uantitative 6ost96rocessing o! the results o! $D

simulations.

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(nce the solution is converged7 the solver writes all the data related to grid7

boundary conditions and !low 6arameters are stored in the result !ile. It is a binary

!ile7 which can be o6ened by loading result !ile in $@9Post7 and the results are

analyed. The 6er!ormance o! com6ressor stage is studied by using suitable

macros. The various 6lots are drawn and listed in results. Using the !unctioncalculator o6tion 6arameters like ,ass !low rate7


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6.RESULTS AND DISSCUSSION

3.2*&N&)A'

The simulated investigation on the im6eller o! a centri!ugal !an are 6resented and

inter6reted in this cha6ter. Data e>traction and inter6retation !orm a very im6ortant

6art o! $D analysis to show con!ormity o! simulated data with the e>6erimental

results

The chosen centri!ugal !an has an im6eller diameter o! // mm and an e>it width o!

31 mm.

The simulation is conducted on the im6eller o! a !an at various s6eeds. The various

s6eeds that were considered are Design S6eed o! 245/ )P,7 3/ )P, and =//

)P, r6m. low is analysed !or di!!erent !low rates. The !low rates considered are

57357 /7 2//7 22/7 2=/721/.

The di!!erent 6arameters chosen !or com6arison areO

2;


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2;


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increases !or various !low rates.

3.=.1


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6.3RESULTS

6.3.V#"%e' o)$#*e(

!oe

!oe


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6.3.3V#"%e' o)$#*e(

+er

+#''#=

e, !%.m F"o> !oe


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PRESSURE

Total 6ressureO9

Total 6ressure !or 3/ )P, at / !low Total 6ressure at 3/ )P, at 2// !low

Total 6ressure !or 3/ )P, at 21/ !low

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)elative 6ressureO9

)el. 6ressure !or 3/ )P, at / !low )el. 6ressure at 3/ )P, at 2// !low

)el. 6ressure !or 3/ )P, at 21/ !low


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Static 6ressureO9

Ps !or 3/ )P, at / !low Ps !or 3/ )P, at 2// !low

Ps !or 3/ )P, at 21/ !low

3


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Pt at 3/ )P, at 2// !low Pt at 245/ )P, at 2// !low

Pt at =/// )P, at 2// !low


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VELOCITY


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MERIDONIAL PLOTS

$ontour 6lot o! Pt at 3/ )P, at / $ontour 6lot o! Pt at 3/ )P, at 2//

$ontour 6lot o! Pt at 3/ )P, at 21/

32


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STREAM LINE PLOT


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BLADE LOADING

At 245/ )P, and / !low O9

At 245/ )P, and 2// !low O9

At 245/ )P, and 21/ !low O9

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At 3/ )P, and / !low O9

At 3/ )P, and 2// !low O9

34


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At 3/ )P, and 21/ !low O9

At =/// )P, and / !low O9

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At =/// )P, and 2// !low O9

At =/// )P, and 21/ !low O9

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6.2 GRAPS

PRESSURE RISE VS MASS FLOW

3


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TOTAL PRESSURE VS MASS FLOW RATE

33


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EAD COEFFICIENT VS MASS FLOW RATE

3


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TOTAL EFFICIENCY VS MASS FLOW

/


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SAFT POWER VS MASS FLOW AT ;61 RPM

FLOW COEFFICIENT VS EAD COEFFICIENT

2


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;.CONCLUSIONS

A low s6eci!ic s6eed centri!ugal !an was designed !or the given !low and

head conditions. The !an im6eller was modelled using ANS+S Turbo *rid and was

analysed using $@ 6ackage.

The !an 6er!ormance was evaluated and studied !or di!!erent !low

conditions covering design and o!!9design 6oints o! o6eration and also !or di!!erent

s6eeds.

The 6er!ormance is seen to be !ollowing the normal trend !or a low s6eci!ic

s6eed !an and the !low and head curve shi!ts u6wards with increasing s6eed.

The im6eller e!!iciency seen to be ma>imum at the design 6oint and decreasing

at o!!9design conditions. The e!!iciency is !ound to be above /7 this is because

the windage losses7 !rictional losses have not been accounted.

The di!!erent contour and vector 6lots as well as the blade loading curve are

included !or ty6ical cases o! design and o!!9design conditions.

The 6ressure rise is seen to increase uni!ormly along the im6eller 6assage.

1.SUGGESTIONS FOR FUTURE WORK

This work may be e>tended by varying the number o! im6eller blades and

also by including the volute casing to get the total !an 6er!ormance.

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.REFERENCES

a; Prithvi )a? 8 *o6ala -rishnan Treatise on Turbo ,achine

b; Wol!gang Scheer Introduction to Turbo ,achinery

c; #al?e7 (.D. A $ontribution to the 6roblem o!

Designing )adial Turbo ,achines

d; P!leiderer Die kreisel 6um6en

e; Wiki6edia.org

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