# Invicisd compressible flow over cylinder 2D

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December 1, 2012, 19:47
Invicisd compressible flow over cylinder 2D
#1
New Member

wesam
Join Date: Sep 2012
Posts: 23
Rep Power: 7
hi

i have a problem in negative values of CD.

Images are shown for the solution process.

thank you
Attached Images
 cylinder.jpg (96.9 KB, 25 views) Drag convergence.jpg (69.7 KB, 21 views) Negative cd solution.jpg (103.0 KB, 16 views) operating pressure.jpg (95.1 KB, 17 views) pressure Far-field.jpg (94.1 KB, 17 views)

 December 4, 2012, 04:12 #2 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,250 Rep Power: 34 your solution isn't converged (your second picture can prove it, since it is still oscillating) disable the "check convergence" at 1e-3 and let iterate. Just break the iterations once your cd has a constat value __________________ In memory of my friend Hervé: CFD engineer & freerider

December 4, 2012, 14:52
#3
New Member

wesam
Join Date: Sep 2012
Posts: 23
Rep Power: 7
HI MAX

i have done what you said to me.but the result of CD is negative and it is impossible it must be positive.(aerodynamic basic).

where is the error.
thank you Mr.MAX
Attached Images
 Untitled.jpg (66.7 KB, 6 views) cd.jpg (64.9 KB, 7 views) Untitled2.jpg (101.4 KB, 6 views) Residuals.jpg (92.7 KB, 7 views)

 December 5, 2012, 02:12 #4 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,250 Rep Power: 34 I don't know... check if the velocity and pressure distribution are ok Check also the forces on your 2d-cylinder and compute manually your Cd And also check if your axis are well defined, especially the one for Cd should be in same direction as fluid is flowing (it is the only explanation for negative value, since others are positive) wesam likes this. __________________ In memory of my friend Hervé: CFD engineer & freerider Last edited by -mAx-; December 5, 2012 at 02:29.

 December 10, 2012, 19:39 #5 New Member   wesam Join Date: Sep 2012 Posts: 23 Rep Power: 7 thank you MAX please check your e_mail. I am in trouble you only one can help me. thank you

December 11, 2012, 02:31
#6
Super Moderator

Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,250
Rep Power: 34
Quote:
 Originally Posted by wesam thank you MAX please check your e_mail. I am in trouble you only one can help me. thank you
I don't have any email
__________________
In memory of my friend Hervé: CFD engineer & freerider

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