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March 21, 2011, 08:27 |
lift and drag coefficient of box
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#1 |
Member
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Hello!
I visualized turbulent flow around a box. I try to calculate lift and drag coefficients. In controlDict I add functions { forces { type forceCoeffs; functionObjectLibs ( "libforces.so" ); outputControl timeStep; outputInterval 1; patches ( box ); rhoName rhoInf; log true; rhoInf 1.2041; CofR ( 0 0 0 ); liftDir (0 1 0); dragDir (0 0 1); pitchAxis (0 0 0); magUInf 4.0; lRef 0.8; Aref 0.64; } } At the end of time, I have a file forces. The results are wrong: Cd=-1.85 Cl=-12665 Size of box: fin is 0.8m Size of tunnel: fin is 5.6m, heigh is 2.4m Where I have a mistake? |
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March 30, 2011, 11:12 |
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#2 |
Member
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Nobody has problems with problem like this?..
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March 30, 2011, 11:44 |
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#3 |
New Member
Fatih
Join Date: Sep 2010
Location: Hamburg
Posts: 12
Rep Power: 16 |
hi akuji,
if your simulation is 2D, then you have to check your Aref. lets say your 2D mesh is only 1 mm thick than you have to set your Aref Aref=lRef*thickness-of-mesh=0.8/0.001 Edit: Sorry, it should be Aref=0.8*0.001 not 0.8/0.001 Last edited by ang_dipl_ing_fd; March 31, 2011 at 07:15. |
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March 31, 2011, 07:18 |
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#4 | |
Member
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Quote:
And...if my mesh is 3D? (It's really 3d) |
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March 31, 2011, 16:28 |
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#5 |
New Member
Fatih
Join Date: Sep 2010
Location: Hamburg
Posts: 12
Rep Power: 16 |
in openfoam it is always 3D. with 2D i meant that front and back patches are empty. the 3rd dimension is the thickness of the volume.
best regards |
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April 7, 2011, 06:39 |
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#6 |
Member
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Well, I find a right solution. But I still have a question.
rhoName rhoInf; log true; rhoInf 1.2041; CofR ( 0 0 0 ); liftDir (0 -0.01 0); dragDir (0 0 1); pitchAxis (0 0 0); magUInf 4.0; lRef 0.8; Aref 0.64; Why I need to set liftDir 0.01? |
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April 7, 2011, 06:51 |
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#7 |
Member
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And one more question
I find information, that wrong to calculate lift coefficient if square of windward surface is not equal of square of downwind surface. What to do in this case? |
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