[jki]

Hi,

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

Thank's

[immortality]

hi
Search at this site.i saw a comlete thread about lift and drag cefficients here.
Be successful.

[Matt1986]

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

[jki]

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.

[Matt1986]

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

[jki]

Hi Matthias,

My case is RAS,

The cd is too high,

Can you take a look?

Thanks

[Matt1986]

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

[Matt1986]

Hi,

Have you solved the problem?

[jki]

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