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how to calculate the drag force on a 3D sphere in OF?

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Old   May 5, 2015, 16:33
Default how to calculate the drag force on a 3D sphere in OF?
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David Long
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Hi Foamers,

I want to test the drag coefficient of regular (e.g. sphere) and irregular objects using the CFD method.

The problem is that how to calculate the fluid force acting the Object.

A still sphere is in the fluid and the velocity and pressure field are solved (currently pimpleFoam):



The resulting force would be: (assuming the sphere has N sub-surfaces, treated as wall)
Quote:
F_fluild = Sum(Pi * Ai* n), i = 1, 2, .... N
where Pi/AI- pressure/area of ith surface of the sphere/obstacle, n the normal of ith surface .

If we subtract buoyancy force Fb from F_fluid,
Quote:
F_(drag/life) = F_fluid - Fb
The issue is: how to loop on the certain boundary and access the pressure or velocity information on this boundary (object/obstacle).


Any tips or recommendation would be highly appreciated.

thanks in advance!

Last edited by keepfit; May 5, 2015 at 19:00.
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Old   May 6, 2015, 05:20
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Tom Fahner
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I would suggest to use the forces and forceCoeffs functionObjects. There are many threads on this forum that discuss it....
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Old   May 6, 2015, 12:04
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David Long
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Quote:
Originally Posted by tomf View Post
I would suggest to use the forces and forceCoeffs functionObjects. There are many threads on this forum that discuss it....
thanks tomf, I will give a try on the library fucntions.
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