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Old   December 28, 2012, 05:49
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jki
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Joaquim Monteiro
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Hi,

How can I calculate the drag coeficient of a circular cylinder?

Thank's
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Old   December 28, 2012, 09:30
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hi
Search at this site.i saw a comlete thread about lift and drag cefficients here.
Be successful.
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Old   January 5, 2013, 08:38
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Matthias K.
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Hi,

You have to insert the function forceCoeffs into your control.dict. in the folder system.
Here is a example:

forceCoeffs
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
patches (patchname); //change to your patch name of the cylinder
pName p;
UName U;
rhoName rhoInf;
rhoInf 1.225; //Density of the fluid
CofR (0 0 0);
liftDir (0 0 1);
dragDir (1 0 0);
pitchAxis (0 1 0);
magUInf 0.0243243243; //velocity
lRef 0.0555; //reference length for forces
Aref 1.11e-3; //reference surface of the cylinder
outputControl timeStep;
outputInterval 10; //every x timesteps =>one drag coefficient
}

Then you are able to calculate the drag coeficients

Hope that helps

Regards,
Matthias
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Old   January 6, 2013, 06:06
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Thanks Matthias,

I'm a newbie in OpenFoam.

I try and it works.

Now the problem is that the value of cd is too high in compare with the academics work there i saw.

Perhaps you know what's my problem.
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Old   January 6, 2013, 08:44
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Hi,

Is your case LES or RAS?
Have you modified a existing tutorial?
Have you checked your boundary conditions?
Can you upload your case, that i can have a look?
I am doing LES cd calculations of a 2d cylinder, at the moment.

Low Reynolds LES Simulation questions

Regards Matthias
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Old   January 7, 2013, 05:54
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Hi Matthias,

My case is RAS,

The cd is too high,

Can you take a look?

Thanks
Attached Files
File Type: zip re4.zip (15.6 KB, 13 views)
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Old   January 9, 2013, 18:30
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Hi,

I think your epsilon value is too high.
Your value is 1.01.
With a viscosity of 1e-3 and a velocity of 0.2 m/s is should imho be much smaller.

Regards Matthias
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Old   January 21, 2013, 10:14
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Hi,

Have you solved the problem?
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Old   January 22, 2013, 05:13
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hi,

i can't solve the problem.

now I'm in exams, and I haven't been working on the problem.

you got see any errors in my files.

thanks
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