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jcwldy
Posts: 4
Registered: ‎01-11-2013

drag forces on a sphere

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01-16-2013 07:52 AM

I am conducting a sample simulation on a sphere in a constant flow path of water.  I was thinking I could run a simple simulation of a sphere in a constant flow and use the wall calculator to extract the drag forces caused by the fluid flow.  I was then planning to use Hydrodynamic force equations on a sphere and compare the calculated forces with the forces returned from the simulation.

 

I know the water density, fluid velocity, sphere diamarer, and fluid dynamic viscosity.  From there I calculate the Reynolds number.  I then use the Re to find the drag coefficient using the "Cd vs Re of a sphere plot".  I then use Fd=.5*density*velocity^2*drag coefficient*projected sphere area, to calculate drag force.

 

The problem that I am having is that my drag forces from the simulation are about double that of what I calculated.  If I assume a sphere diameter of 3.94 in and Re of 99,597.2, I get a Cd of around 0.4245 and a force of .374 lbs.

 

I enclose a continuum around a 3d sphere, mesh the sphere and continuum using a very dense mesh, Adv 5 and can not get a result near the calculated one. 

 

Am I using the wrong approach?

 

Thanks

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