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Old   May 3, 2010, 09:08
Default 3-D wing analysis problem
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Arjit Arora
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Hi guys!

Facing a problem while doing the analysis of a 3D wing (finite).

The geometry has been meshed in gambit. I have used a structured boundary layer.. and the remaining mesh too is structured. Used the cooper scheme to get from 2D to 3D.
The fineness of the boundary layer had to be reduced because some of the elements were getting a negative volume or were getting too skewed.

Eventually, got the right mesh (according to the mesh check of Fluent). But on running analysis, got some really wrong results..

The conditions: 1. Laminar
2. velocity inlet at 15m/s
3. air, incompressible- constant density
4. outlet boundary layer - "outflow"

And the results that I got were quite alarming. All the pressure contours on the wing were pointing downwards!!

1. What could be the reason for this?
2. Could I use better boundary conditions?

Thanks!
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Old   August 3, 2012, 06:04
Default velocity inlet in fluent
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hhh
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kumar
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Dear friends,
In fluent, For analysis of 2D naca0012 airfoil velocity inlet we give vcostheta in x component & vsintheta in y component, v is inlet velocity.

1)here i start analysis of 3D wing, for that i take naca 0012 airfoil chord '1'& extrude 100mm, in gambit and analysis in fluent i have doubt how to set velocity inlet, here i consider my velocity is 3m/s, then what is xyz component in inlet velocity boundary condition,please let me know.

2)if you consider 3D wing, (vtantheta for z component) is correct or wrong, please let me know.

2) how to find angle of attack for 3D wing? please let me know
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Old   August 3, 2012, 09:46
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Quote:
Originally Posted by arjit View Post
Hi guys!

Facing a problem while doing the analysis of a 3D wing (finite).

The geometry has been meshed in gambit. I have used a structured boundary layer.. and the remaining mesh too is structured. Used the cooper scheme to get from 2D to 3D.
The fineness of the boundary layer had to be reduced because some of the elements were getting a negative volume or were getting too skewed.

Eventually, got the right mesh (according to the mesh check of Fluent). But on running analysis, got some really wrong results..

The conditions: 1. Laminar
2. velocity inlet at 15m/s
3. air, incompressible- constant density
4. outlet boundary layer - "outflow"

And the results that I got were quite alarming. All the pressure contours on the wing were pointing downwards!!

1. What could be the reason for this?
2. Could I use better boundary conditions?

Thanks!
what is your flow Reynold's No? what is the chord and span of your wing? Is the flow Reynold No really that too low that you are considering it to be laminar?
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Old   August 3, 2012, 09:51
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Quote:
Originally Posted by hhh View Post
Dear friends,
In fluent, For analysis of 2D naca0012 airfoil velocity inlet we give vcostheta in x component & vsintheta in y component, v is inlet velocity.

1)here i start analysis of 3D wing, for that i take naca 0012 airfoil chord '1'& extrude 100mm, in gambit and analysis in fluent i have doubt how to set velocity inlet, here i consider my velocity is 3m/s, then what is xyz component in inlet velocity boundary condition,please let me know.

2)if you consider 3D wing, (vtantheta for z component) is correct or wrong, please let me know.

2) how to find angle of attack for 3D wing? please let me know
You need to consult some book of aerodynamics your basic concepts seems to be not too good but don't worry not a problem....consult "Fundamentals of Flight by Anderson"...apart from this an angle of attack is an angle of attack whether its in 2D or 3D. You will specify the same conditions in 3D as you have done for the 2D case
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Old   August 4, 2012, 04:09
Default velocity inlet in fluent
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Dear cfd seeker,

thanks for your kind response, In fluent, For analysis of 2D naca0012 airfoil velocity inlet(boundary condition) we give vcostheta in x component & vsintheta in y component.


if u consider 3D wing what is z component,(velocity inlet ie boundary condition) i think vtantheta for z component? it is correct or wrong please let me know
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Old   August 4, 2012, 05:42
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Quote:
Originally Posted by hhh View Post
Dear cfd seeker,

thanks for your kind response, In fluent, For analysis of 2D naca0012 airfoil velocity inlet(boundary condition) we give vcostheta in x component & vsintheta in y component.


if u consider 3D wing what is z component,(velocity inlet ie boundary condition) i think vtantheta for z component? it is correct or wrong please let me know
you are wrong, z component will be zero both in 2D and 3D cases....if you just read the basics you will understand what actually angle of attack is.......
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Old   August 5, 2012, 02:40
Default velocity inlet in fluent
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Dear cfd seeker,
thanks for information, i know the definition of angle of attack, i already did 2D analysis of naca 0012, but 3D wing i dont know how to give boundary condition in fluent especially velocity inlet, in my case velocity is 10m/s.

For 3D wing,here i attached three image, which is suitable for my case if v=10m/s, please see my attached image, let me know.
Attached Images
File Type: png image 1.png (17.8 KB, 37 views)
File Type: png image 2.png (22.7 KB, 36 views)
File Type: png image 3.png (24.0 KB, 33 views)
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Old   August 5, 2012, 05:37
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Quote:
Originally Posted by hhh View Post
Dear cfd seeker,
thanks for information, i know the definition of angle of attack, i already did 2D analysis of naca 0012, but 3D wing i dont know how to give boundary condition in fluent especially velocity inlet, in my case velocity is 10m/s.

For 3D wing,here i attached three image, which is suitable for my case if v=10m/s, please see my attached image, let me know.
for 3d case
x-component= 10*cos(AOA)
y-component=10*sin(AOA)
Z=0
AOA= angle of attack
there is no difference in boundary conditions for 2d and 3d cases
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Old   August 6, 2012, 03:51
Default velocity inlet in fluent
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Dear cfd seeker,
thanks, for your help, then which image i have to select and give velocity inlet,let me know.
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Old   August 6, 2012, 10:46
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Quote:
Originally Posted by hhh View Post
Dear cfd seeker,
thanks, for your help, then which image i have to select and give velocity inlet,let me know.
image no.2
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Old   August 7, 2012, 02:26
Default velocity inlet in fluent
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hhh
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Dear cfd seeker,

thanks for your help.
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Old   August 18, 2012, 14:22
Default velocity inlet in boundary condition
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Dear cfd seeker,
i am doing steady analysis in for my 3D wing, for that i mesh in gambit & import in fluent. i consider solver is pressure based &my model is laminar flow, Know value i have is velocity= 5m/s, area=0.0102 m2, length=0.065m.

[boundary condition-velocity inlet, pressure outlet, remaining faces are symmetry& wing is wall]

In fluent i dont how to set velocity inlet, for v=5m/s, i dont which velocity specification method is i have to selected under dropdown?

please help me i get confused while read the fluent user guide
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Old   June 15, 2013, 14:01
Default uneven flow at aoa
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Quote:
Originally Posted by cfd seeker View Post
for 3d case
x-component= 10*cos(AOA)
y-component=10*sin(AOA)
Z=0
AOA= angle of attack
there is no difference in boundary conditions for 2d and 3d cases
i am doing a similar type of simulation
but whet i set inlet velocity at positive angle of attack
i get the flow accumulated at upper surface of wind tunnel
giving uneven flow throughout the wind tunnel ( higher velocity at upper surface of wind tunnel and lower velocity at lower surface of wind tunnel)
and i have chosen boundary conditions as symmetry for both upper and lower surface of wind tunnel(air domain around wing is rectangular box)
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Old   June 16, 2013, 05:47
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hhh
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Greetings bikalpa10

i didn't understand your problem what is your domain size?
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Old   June 17, 2013, 14:39
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thanks kumar
but actually i figured out where i was going wrong
i choose boundary condition for wind tunnel wall as velocity inlet and that worked out for me.
thanks anyways
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