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?