boudayer layer group 1 mtech 15 17

8/17/2019 Boudayer Layer Group 1 Mtech 15 17

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Motilal Nehru National

Institute of Technology, Allahabad

Lab Report OnFlow Over Flat late in !ind

Tunnel"ub#itted to $ %r& A& R& au

%r& '& (& atel

"ub#itted by$ )roup *


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Overview

• Ob+ectives• Introduction•

Apparatus• Test procedure• Approach• alculations and results• o#putational analysis• Observations


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Objectives

• To e-peri#entally deter#ine velocity profile on a s#oothflat plate at various distances&

• o#putational analysis of flow over flat plate inside asubsonic wind tunnel&


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Introduction

• !hen real fluid flows past a solid body or a solid wall, thefluid particles adhere to the boundary and condition of no slioccurs&• This is the region where viscous forces are do#inant&• I#portant ter#s in boundary layer *& No slip condition.& La#inar boundary layer

/& Transition boundary layer 0& Turbulent boundary layer •. La#inar sub layer •. 1uffer layer •. Turbulent layer


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Turbulent Boundary Layer


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Growth of boundary layer over flatplate


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Test Apparatus Schematic diagram


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Test Apparatus wind tunnel! "omponents

• It is a device in for# of a long duct for producing a #ovingairstrea# for e-peri#ental purposes&

• It is used to study the effects of air #oving past solidob+ects 2 in our case it is a flat plate3&

• There are three essential co#ponents$*&4ffuser .& !or5ing section

/& %iffuser0&%riving unit


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#$ %ffuser :•. This is placed upstrea# of the wor5ing section&•. In it the fluid is accelerated fro# rest to appro-i#ately atupstrea# end to the re6uired conditions at the wor5ingsection&

&$ 'or(ing section)•. It is here that the #odel is placed is in the air strea# leavingthe downstrea# end of the effuser and the re6uiredobservations are #ade&

•. The wor5ing section consists of accessories to hold theinstru#ents and #odels and devices for facilitating the #otionof the #odel in all directions relative to airstrea# &


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*$+iffuser )

• The function of the diffuser is to recover the 5inetic energy of the airstrea# leaving thewor5ing section efficiently as possible

• Test section$ length 789&8:9&/8

,$ +riving unit)

• ower is supplied continuously to #aintain the flow through suction 2atvariable condition3&

• This is done using a fan and a #otor&• ower is given by . #otors of &;75w and .:88 rp# each&•

'elocity of inco#ing air can be controlled by ad+usting the controlvalve which further controls the suction by #aintaining the upstrea#opening&


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Accessories #! -itot Static Tube

• itot tube is a pressure #easure#ent instru#ent used to #easure fluid flowvelocity&

• "tagnation pressure 8c# - :&• For#ula used to convert reading in ter#s of velocity


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Multitube#ano#eter

Flat late


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Test -rocedure

•

The flat s#ooth surface was 5ept on a stand fir#ly, at the testsection of the wind tunnel&• The wind tunnel was set up with a itot tube, and the flat plat#ade #ovable so that analysis could be #ade at different sectionfro# the leading edge, attached to a #ulti tube #ano#eter to getthe pressure differentials&• Then the wind tunnel was turned on, and the #ano#eter wascalibrated&• The pressure differentials readings were ta5en at 0 points withthe boundary layer gradually increasing By 2distance #easuredfro# the surface3&• The pressure difference was noted carefully&• The test was repeated ad+usting the pitot tubeat 7, *8, *7, .8 c#

fro# the leading edge of the glass plate&


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Approach • !e have calculate the readings on the points2#entioned in previous slide3 and on four different velocities&

• To reduce the no& of readings we have ta5en the help of

Minitab "oftware in which Taguchi #ethod was used&• Nu#ber of para#eters$• 'elocity2u3&• %istance fro# leading edge2-3&• %istance fro# plate surface 2y3&• No& of levels used in each para#eters < 0


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"o fro# Taguchi chart

1y using above values the table provides the orthogonal arrayLC*> table &


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Taguchi orthogonal array L0#1


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.initab result• The result of Taguchi method had been validated

from Minitab Software.


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• !"# array has reduced the #$ readings %that hasto be calculated& to "# readings.

'(periment Velocity%m)s& * distance%m& + distance%m&" ", .,- .,,

", .", .,,$/ ", ."- .,,#$ ", . , .,,0- "- .,- .,,$# "- .", .,,1 "- ."- .,,00 "- . , .,,#2 , .,- .,,#", , .", .,,0"" , ."- .,," , . , .,,$"/ - .,- .,,0"$ - .", .,,#"- - ."- .,,$"# - . , .,,


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Shortcomings of taguchi

• Taguchi #ethod is #ainly used to reduced the no& ofe-peri#ents where few variables contribute significantly&

• 1ut in our e-peri#ents each of the variables have e6ualcontribution&

• "o taguchi #ethod was not co#patible with the ob+ectiveof our e-peri#ent as it was not providing the sufficient no&of readings to plot a graph different variables&


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Approach • 1ecause of non applicability of taguchi we proceeded withthe calculation of >0 readings&

• For that we have ta5en four velocities and for each velocity

there were four different - values and at each - velocitieswere calculated at different y values.


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Observations and "alculations

3,." ,." ,./ ,.- ,.1 ,.2 "." "./ ".-,

,.-

"

".-

.-

At u= 10m/s

4t (5.,-m4t (5,."m4t (5,."-m4t (5,. ,m

u/U

y/δ


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, ,.- " ".-,

,.

,.$

,.#

,.0

"

".

".$

".#

At u= 15m/s

at (5.,-m

at (5.", mat (5."- mat (5. , m

u/U

y/δ


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, ,.- " ".-,

,.-

"

".-

.-

At u= 20m/s

at (5 .,- mat (5 .", mat (5."- mat (5. , m

u/U

y/δ


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3,." ,." ,./ ,.- ,.1 ,.2 "." "./ ".-,

,.-

"

".-

.-

At u= 25m/s

at (5 .,- mat (5 .", mat (5 ."- mat (5 . , m

u/U

y/δ


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Boundary layer at different velocity

, ,.,- ,." ,."- ,. ,. -,

,.-

"

".-

.-

Boundary Layer Thickness

4t 65",m)s4t 65"-m)s4t 65 ,m)s4t 65 - m)s

x in m

δ in mm


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"omputational Analysis

• Flat plate was analyDed for the above #entioned velocitiesin Ansys Fluent& 'elocity were calculated at the above#entioned points.

Geometry)

%i#ension for geo#etry were in accordance to thelaboratory apparatus


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Geometry with domain used in CFD analysis

Meshing $Mesh was generated by siDing techni6ue with bias near the plate resulting finer #esh& !hile cowas #aintained away fro# the plate&

Eoo#ed view of #esh near plate


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Mesh %etails $tatistics !aximum "a#ue !inimum "a#ue

ke$ness ". /'3 "./,'3",

Aspect ratio /#.2$- ".,"2

%rtho&ona#ity ,.// "

"olver "ettings$• 1ecause of the turbulent flow standard 5 epsilon #odel was used wi

standard wall function for near wall treat#ent& !ith defaults constantssettings&

• 7oundary conditions: 4t inlet: velocity inlet Velocities given 8 ",9 "-9 ,9 - m)s 4t outlet: pressure outlet

auge pressure 8 ;ero Pascal.


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'elocity and ressure contoursPressure contours :

Total pressure is the summation of the static and dynamic pressure.


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'elocity and ressure contoursVelocity contours :


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'elocity and ressure contoursVelocity vector

contours :


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o#parison b@w e-peri#ental and co#putationalresults

, $ # 0 ", ",

,

,At #2 m3s

e(pcom

U

y

, $ # 0 ", " "$ "#,

,

,

At #4 m3s

e(pcom

U

y


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, - ", "- , -,

,

,

,

,

At &2 m3s

e(pcom

U

y

, - ", "- , - /,,,,,,

At &4 m3s

e(pcom

U

y


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Observations• !ith increase in a-ial distance fro# the leading edge , boundarylayer thic5ness increases &

• !ith increase in velocity ,at sa#e a-ial distance , 1oudary layerthic5ness decreases &

• Total ressure increase with increase in lateral height fro# plate &

• "tatic pressure re#ain constant throughout the do#ain e-ceptat the leading edge &


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• Than 6

boudayer layer group 1 mtech 15 17

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