# Flow over square Cylinder

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January 26, 2014, 15:05
Flow over square Cylinder
#1
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alireza
Join Date: Jul 2009
Posts: 32
Rep Power: 14
Hi
I'm trying to solve flow over a square cylinder at Re=5,20. I used velocity inlet and outlet boundary condition. I solved the problem, But my result was wrong, i don't know why?!?????
I attached velocity and pressure contour. As you can see results is wrong.
This problem is very simple, Re=5, laminar flow and ... . But unfortunately my result is wrong.

can you help me?
Attached Images
 velocity.jpg (64.2 KB, 52 views) pressure.jpg (52.3 KB, 40 views)

 January 26, 2014, 15:10 #2 Super Moderator     Alex Join Date: Jun 2012 Location: Germany Posts: 3,210 Rep Power: 44 How did you make sure that this is a converged solution? And could you post an image of the mesh you used?

January 26, 2014, 15:24
#3
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alireza
Join Date: Jul 2009
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I attached image of mesh and convergence history.
Attached Images
 converge.jpg (43.6 KB, 34 views) mesh1.jpg (94.0 KB, 51 views)

 January 26, 2014, 16:13 #4 Super Moderator     Alex Join Date: Jun 2012 Location: Germany Posts: 3,210 Rep Power: 44 Did you try running more iterations? I would run such a simple case until round-off accuracy is achieved. One thing less to worry about. Judging from the image of the mesh, I recommend using double precision. Did you use velocity inlet, pressure outlet and symmetry boundary conditions?

January 27, 2014, 04:54
#5
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like.no.other
Join Date: Sep 2011
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Quote:
 Originally Posted by alireza_b Hi I'm trying to solve flow over a square cylinder at Re=5,20. I used velocity inlet and outlet boundary condition. I solved the problem, But my result was wrong, i don't know why?!????? I attached velocity and pressure contour. As you can see results is wrong. This problem is very simple, Re=5, laminar flow and ... . But unfortunately my result is wrong. can you help me?
Hi alireza

which parameter is wrong?
Cd?
Cp?

Please send me your case fine, I can help u
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January 31, 2014, 03:12
#6
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alireza
Join Date: Jul 2009
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Quote:
 Originally Posted by flotus1 Did you try running more iterations?
Yes, I did.

Quote:
 Originally Posted by flotus1 Did you use velocity inlet, pressure outlet and symmetry boundary conditions?
I used velocity inlet and pressure outlet. left, top and bottom are velocity inlet and right is pressure outlet. I also used symmetry, but the answer is wrong.

January 31, 2014, 03:17
#7
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alireza
Join Date: Jul 2009
Posts: 32
Rep Power: 14
Quote:
 Originally Posted by like.no.other Hi alireza which parameter is wrong? Cd? Cp? Please send me your case fine, I can help u
Hi
both flow field and Cd are wrong. I check reference value, this is correct but answer is wrong.

February 1, 2014, 14:32
#8
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Alex
Join Date: Jun 2012
Location: Germany
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Quote:
 Originally Posted by alireza_b Yes, I did.
Please run the case in double precision untill the residuals level out and show the results (residuals+contour plots).
If still not satisfied with the results, use a mesh that is more suitable for low Reynolds number flows. Its the high aspect ratio cells that cause slow convergence. You dont need such a high resolution near the wall.

One more thing: dont expect to get a value for the drag coefficient that matches any reference solution for a square cylinder in free stream.
The extent of the computational domain is not enough for low reynolds number flows.
Quote:
 left, top and bottom are velocity inlet
Top and botom should be symmetry boundary conditions.

Last edited by flotus1; February 1, 2014 at 18:13.

 February 5, 2014, 05:16 #9 New Member   Join Date: Jan 2014 Posts: 5 Rep Power: 11 i think your fine mesh area has not properly defined because it will concentrate result in fine mesh area . also one more point is that whenever their is flow over bodies then it will shows laminar region somewhat distance along the length not to the the its near by wall region..

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