POSTGRADUATE Flow Over a Cylinder_final

8/18/2019 POSTGRADUATE Flow Over a Cylinder_final

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Section A To be completed by the studentStudent Full Name

MAHMUD AL HASSANStudent ID Number

EAU 1015649Lecturer Name

AMNA EL CHEIKHModule Name and ode Computational Fluid Dynami! "CFD#

Assignment Due date

$t% Ap&il '016Assignment Title St(ady )o* o+(& a ylind(&


2/23

Aerospace Engineering Department Graduate Program

Computational Fluid Dynamics (CFD)

(11 Feb to 15 Feb 201)

Pro!ect "2

Steady Flow Over A Cylinder

Done by#

$ame %D

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&a'mud Al assan EA1015*+

,ubmitted to#

Amna El C'ei-'

Due Date# April .t' / 201

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Table of Contents

1.0 Introduction ...........................................................................................................4

1.1 Equations........................................................................................................41.2 Background.....................................................................................................41.3 Objectives........................................................................................................5

1.4 Theor.............................................................................................................51.5 !ssu"#tions....................................................................................................5

2.0. $ethods ...............................................................................................................5 2.1 %eo"etr.........................................................................................................5 2.2 $esh................................................................................................................& 2.3 'a"ed (e)ection and $ateria)........................................................................* 2.4 Boundar +ondition.........................................................................................*

2.5 (o)ution and ,esidua)s....................................................................................*

3.0 (tead -)o.........................................................................................................../ 3.0.1 +ontours......................................................................................................./ 3.0.2 ressure +ontour...................................................................................../ 3.0.3 e)ocit +ontour........................................................................................... 3.0.4 e)ocit ectour..........................................................................................10 3.0.5 ariation o +# on u##er and )oer surace o c)inder..............................11 3.0.& ressure and viscous coeicients on various ve)ocities............................12 3.0.* rag and it coeicient on various ve)ocities............................................13

3.0./ iscussions and !na)sis...........................................................................14 3.0. escre#ancies beteen nu"erica) and E6#eri"enta) data.......................15

4.0.0 7nstead -)o ....................................................................................................... 1&4.0.1 !ni"ation...................................................................................................1&4.0.2 ariation o )it coeicient or 0.2s..............................................................1&4.0.3 ariation o )it coeicient or 1s.................................................................1*4.0.4 ressure +ontour.......................................................................................1/4.0.5 e)ocit +ontour.........................................................................................1/4.0.& iscussion.................................................................................................. 1

5.0 +onc)usion............................................................................................................ 1/

&.0 )ots8Tab)es.......................................................................................................... 1/&.1 ,eerences and Bib)iogra#h....................................................................................1/

!##endi6.......................................................................................................................... 1

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10 %ntroduction

Regardless of experimental and numerical studies almost over few decades, flow around a

circular cylinder still remains a problem of research in fluid mechanics.Flow around bodies such as circular cylinders are extensively used in the field of engineering.

Buildings, chimneys, cooling towers and tubes are just few examples of these applications.

This assignment aims the study of flow over a circular cylinder in a steady and unsteady stream.

11 Euations

The governing equations for analysis of teady problem comprises of continuity equation,

!avier"to#es equation $x and y components for two dimensional problem%.These equations are based on fundamental principle of conservation of mass, momentum.

The Na$ier%Sto&es e'uations (or unsteady )o*

&ass conservation $continuity%'

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12 ac-ground

The flow past a two"dimensional cylinder is one of the most studied of aerodynamics. (t isrelevant to many engineering applications. The flow pattern and the drag on a cylinder are

functions of the Reynolds number Re D ) U � D* ν, based on the cylinder diameter D and the

undisturbed free"stream velocity U � . The Reynolds number represents the ratio of inertial to

viscous forces in the flow. The drag is usually expressed as a coefficient C d ) d *$+ρU � D%, where

d is the drag force per unit span.

13 4b!ectie

The main objective of this problem analysis is to understand the flow in a - driven cavity in

terms of numerical, physical and mathematical aspects, along with a very brief literature review

on analytical and numerical studies.

• To analy,e actual )uid motion o$er a circular cylinder-

• To analy,e pressure and $iscous coe.cients-

• To analy,e li(t and drag coe.cients at $arious )o* $elocities-

• To analy,e $ariation o( li(t coe.cient /cl0 (or time steps o( -!s and 1s(or unsteady )o*-

1* 6'eory

circular cylindrical domain is used for this ansys simulation. The effects that the cylinder hason the flow extend far.The outer cylindrical boundary diameter is set to be /0 times as large as

the diameter of the inner cylinder. That is, the outer boundary will be a circle with a diameter of /0 m and inner to be of 1m.

15 Assumptions

t a very low Reynolds number $Re 2 1% the flow across a cylinder is steady and symmetrical in

both upstream and downstream. s Reynolds number increases, the upstream and downstreamsymmetry disappears leading to the formation of two vortices.

20 &et'ods

Ansys 12- Fluent so(t*are is being used to carry out the analysis (or both steady

and unsteady )o*- Microso(t 34cel !1" is used to generate graphs and tables-

21 Geometry

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Fig 1.3 #etch diameter of the cylinders

Fig 1.1 chematic s#etch of geometry $nsys 1/.3%

2.2 Mesh

Fig 1. &esh diagram $nsys 1/.3%

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Fig 1.4 &esh si5e $nsys 1/.3%

The geo"etr is "eshed ith 14400 e)e"ents. The geo"etr #roduces 14&40 nodes. $a##ed

ace "eshing and edge si9ing &0 is used. Bias actor o 30 used in to increase the nu"ber o

e)e"ents )ocated c)ose to the inner c)inder.

23 $amed ,elections and &aterial Properties

-ensity, 6 )1 #g*m74 and 8iscosity, 9) 3.3: #g*m.s.

Inlet6 outlet6 upper and lo*er

2* oundary Conditions7initial conditions

velocity inlet boundary condition. ;eft half of the outer boundary as a velocity inlet with a

velocity of 1 m*s in the x direction. pressure outlet boundary condition for the right half of the

outer boundary with a gauge pressure of 3


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301 Contours

302 Pressure contour

Fig .3


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303 9elocity Contour

Fig .1 8elocity =ontour teady case $nsys 1/.3%

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30* 9elocity ector

Fig .1 8elocity 8ector teady case $nsys 1/.3%

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305 9ariation o: t'e pressure coe::icient on t'e upper and lo;er sur:aces o: t'e cylinder

1m7s

,a&iation o- .&(!!u&( o(/i(nt on upp(& and lo*(& !u&-a(!

lo*er upper

>raph 1.3 8ariation of the pressure coefficient on the upper and lower surfaces of the cylinder

1m*s

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30 Pressure and iscous coe::icients on arious elocities

05m7s

Table 1.3 8ariation of the pressure and viscous coefficient of the cylinder 3.:m*s

1m7s

Table 1.1 8ariation of the pressure and viscous coefficient of the cylinder 1m*s

2m7s

Table 1. 8ariation of the pressure and viscous coefficient of the cylinder m*s

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30. E::ect o: drag and li:t on arious elocities

D&a o(/i(nt +! It(&ation!

-+ m9s

1m9s

! m9s

>raph 1. 8ariation of the drag coefficient vs (terations 3.:m*s,1m*s and m*s.

Li-t Co(/i(nt +! It(&ation!

-+ m9s

1 m9s

!m9s

>raph 1.4 8ariation of the lift coefficient vs (terations 3.:m*s,1m*s and m*s.

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30< Discussions and Analysis

reen represents velocity away from

the cylinder. s the velocity get closer, the color changes to blue. Fluid element particles on the

surface of the cylinder is stagnant which means velocity ) 3.This phenomenon is called

a stagnation point . tagnation point observed at the front of the cylinder and flow separation at

the rear. s the velocity magnitude increases a red color is observed, which is at the top and bottom. 8elocity along the cylindrical surface is parallel which is tangential. 8elocity, and

velocity magnitude, are symmetric about a hori5ontal line through the center of the cylinder.

8elocity 8ector teady case

The flows are seen to be practically symmetric.


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30+ Discrepancy comparison bet;een analytical and numerical solutions and e=planation

>6'e comparison is done in relation to t'e study and approac'es by E=perimental ,tudies

on Flo; C'aracteristics around Circular Cylinder in ,teady and nsteady Flo;?

?eong"Bin ;ee, Aoo"yun Rho, u"wan ?un, Cyu"ong Cim and -ong"o ;eechool of &echanical and erospace Dngineering

eoul !ational Eniversity, (nstitute of dvanced erospace Technology

an :/"1, hinlim"dong, >wana#">ueoul, Republic of Corea

>raph 4.0 =p in teady flow $Research raph 1.3 8ariation of the pressure coefficient on the upper and lower surfaces of the cylinder

1m*s

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% 'ae compared t'e Pressure coe::icients ;'ic' s'o;s a similarity in bot' t'eir and my

alue

*00 nsteady Flo;

e have duplicated the model #eeping all parameters of geometry boundary conditions and mesh

same as steady flow over a cylinder , except changing the viscosity to G.444x137"4 #g*m.s.

(n solution we have selected a transient system, as the initial conditions are set at t)3.

*01 Animation

Fluid )o* analysis aims to determine the relationship bet*een pressure and)o* $elocity by sol$ing 3'uation 16 *hich is sub:ect to a geometric boundarycondition6 i-e-6 the inter(ace sur(ace at *hich a )uid contacts a solid ob:ect-

As $ery small une$en roughness is una$oidably distributed o$er the *holesur(ace o( a solid ob:ect6 )uid particles are completely captured on the solidsur(ace due to the $iscosity o( the )uid- This property o( )uids leads to a $eryimportant assumption such that a condition o( ,ero )uid $elocity /i-e-6 no slip0is achie$ed o$er the *hole sur(ace o( a solid ob:ect-

The )uid in the upper hal( o( this region rotates cloc&*ise6 and the )uid inthe lo*er hal( rotates counter cloc&*ise- This phenomenon is the result o( the so;called generation o( $ortices-

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*02 9ariation o: li:t co e::icient ;it' time step 02s

Fig 4.3 8ariation of the ;ift coefficient $cl% vs Flow Time for time step 3..

*03 9ariation o: li:t co e::icient ;it' time step 1s

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Fig 4.1 8ariation of the ;ift coefficient $cl% vs Flow Time for time step 1s

*0* nsteady Pressure Contour

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Fig 4.


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*0 Discussion

(n both cases investigated, the initial transients die down in the first few time steps and the floweventually reaches a periodic but statistically stationary state.

For 3.s it becomes clear that the flow is oscillatory in nature. =l value oscillates in between H3.133 and "3.133, it@s seen the shedding appears earlier, it gives a better view of oscillation for

the lift co efficient.

For 1s, the curve is smooth for the lift coefficient, compared to the 3.s where the oscillations

due to the vortex shedding.

The values can be calculated with hrouhal number, by calculating the frequency we cancompare our results.s per observation ( could read around pea#s per min, giving a freq of

I.:0e"/,which is close to the literature value.

The pressure and velocity contour shows a turbulence which indicates an increase in Reynoldsnumber.

50 Conclusions

1. -rag forces increases with increasing the velocity of air for cylinders with fixed diameter.. ;ift coefficient distribution about both axis $J and ?% shows that drag and lift forces

about the cylinder are each 5ero.

4. The flow field around the circular cylinder is presented by means of pressure and velocity

magnitude contours.0. The variation of lift coefficient with Reynolds number is one order higher in magnitude

than variation of drag coefficient.

:. (n steady flow changing the velocity shows a steady flow after a number of iterations./. (n unsteady flow the contours represent turbulence which proves the flow to be unsteady

after few time steps.

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0 6ables and Plots# ll plots and graphs are done along the report according to the topic

1 8e:erences and ibliograp'y

1. The comparison is done in relation to the study and approaches by Dxperimental tudieson Flow =haracteristics around =ircular =ylinder in teady and Ensteady FlowK

?eong"Bin ;ee, Aoo"yun Rho, u"wan ?un, Cyu"ong Cim and -ong"o ;ee

chool of &echanical and erospace Dngineeringeoul !ational Eniversity, (nstitute of dvanced erospace Technology

an :/"1, hinlim"dong, >wana#">u

eoul, Republic of Corea

. F. omann, (nfluence of higher viscosity on flow around cylinder, Forsch. >ebiete(ngenieur. 1I $1L4/% 1M13 .

4. =. !orberg, n experimental investigation of the flow around a circular cylinder'

influence of aspect ratio, A. Fluid &ech. :G $1LL0% GI.

0. B. Cumar, . &ittal, . -imopoulous, T.A. anratty, 8elocity gradients at the wall for flow around a

cylinder for Reynolds number between /3 and 4/3, A. Fluid &ech. 44 $1L/G% 434M41L.

/. Thom, The flow past circular cylinder at low speeds,


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Appendi4

Fig 1.3 #etch diameter of the cylinders

Fig 1.1 chematic s#etch of geometry $nsys 1/.3%

Fig 1. &esh diagram $nsys 1/.3%

Fig 1.4 &esh si5e $nsys 1/.3%

Fig 1.0 #etch of Boundary =onditions

Fig .3 raph 1.3 8ariation of the pressure coefficient on the upper and lower surfaces of the cylinder

1m*s

Table 1.3 8ariation of the pressure and viscous coefficient of the cylinder 3.:m*s

Table 1.1 8ariation of the pressure and viscous coefficient of the cylinder 1m*sTable 1. 8ariation of the pressure and viscous coefficient of the cylinder m*s

>raph 1. 8ariation of the drag coefficient vs (terations 3.:m*s,1m*s and m*s.

>raph 1.4 8ariation of the lift coefficient vs (terations 3.:m*s,1m*s and m*s.

Fig 4.3 8ariation of the ;ift coefficient $cl% vs Flow Time for time step 3.sFig 4.1 8ariation of the ;ift coefficient $cl% vs Flow Time for time step 1s

Fig 4. raph 4.0 =p in teady flow $Research

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POSTGRADUATE Flow Over a Cylinder_final