# drag coeficient

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 December 28, 2012, 05:49 drag coeficient #1 New Member   Joaquim Monteiro Join Date: Dec 2012 Posts: 12 Rep Power: 6 Hi, How can I calculate the drag coeficient of a circular cylinder? Thank's

 December 28, 2012, 09:30 #2 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,209 Rep Power: 19 hi Search at this site.i saw a comlete thread about lift and drag cefficients here. Be successful.

 January 5, 2013, 08:38 #3 New Member     Matthias K. Join Date: Oct 2012 Location: Germany Erlangen Posts: 20 Rep Power: 6 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

 January 6, 2013, 06:06 #4 New Member   Joaquim Monteiro Join Date: Dec 2012 Posts: 12 Rep Power: 6 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.

 January 6, 2013, 08:44 #5 New Member     Matthias K. Join Date: Oct 2012 Location: Germany Erlangen Posts: 20 Rep Power: 6 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. http://www.cfd-online.com/Forums/ope...questions.html Regards Matthias

January 7, 2013, 05:54
#6
New Member

Joaquim Monteiro
Join Date: Dec 2012
Posts: 12
Rep Power: 6
Hi Matthias,

My case is RAS,

The cd is too high,

Can you take a look?

Thanks
Attached Files
 re4.zip (15.6 KB, 14 views)

 January 9, 2013, 18:30 #7 New Member     Matthias K. Join Date: Oct 2012 Location: Germany Erlangen Posts: 20 Rep Power: 6 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

 January 21, 2013, 10:14 #8 New Member     Matthias K. Join Date: Oct 2012 Location: Germany Erlangen Posts: 20 Rep Power: 6 Hi, Have you solved the problem?

 January 22, 2013, 05:13 #9 New Member   Joaquim Monteiro Join Date: Dec 2012 Posts: 12 Rep Power: 6 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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