[andrewburns]

I've recently been trying to verify the force outputs of the 'ssimpleFoam' solver I got from another thread on this forum, it's essentially the simpleFoam solver which computes and outputs forces in 3 axes to a file during the simulation.

The problem is a 0.5m diameter 2D cylinder in a flow field of 10m/sec and an nu of 0.05, am I correct in calculating a reynolds number of 100 for this situation?

Re = (10*0.5)/0.05

Taken from a pdf I downloaded off the Nasa technical report server I have a graph of experimental Cd values for infinite cylinders Vs. Re. For a cylinder of Re 100 in steady translation through a viscous fluid I should be getting a Cd of between 1.3 and 1.5 or there-abouts.

At an Re of 100 flow around the cylinder should be laminar, however I ran a laminar simulation with ssimpleFoam and ended up with a drag of only roughly 15N for this cylinder. Using the equation:

Cd = Drag/0.5*rho*v^2*S

Where:

S = 0.5m
rho = 1.225 Kg/m^3
Drag = 15N

Cd = 0.49 Which is far far too low.

I turned on turbulence with a k-epsilon model from this point and ran another 2000 iterations. I noticed a very slow oscillation in the Fx force, I've attached a plot of Fx vs iteration as an example but you can't really see the oscillation as its not really severe.

http://i76.photobucket.com/albums/j2..._iteration.png

The mesh was made in gmsh so it's unstructured. I tried to tighten up the mesh close into the surface of the cylinder and it's fairly detailed so I don't think it's a mesh problem but I can't be certain. Here are pics of the mesh as you zoom in.

http://i76.photobucket.com/albums/j2...whole_mesh.png
http://i76.photobucket.com/albums/j2...mesh_close.png
http://i76.photobucket.com/albums/j2...ltra_close.png

The average final value of drag from the turbulent model solution was about 23.5N, which using the above equation for Cd still only gives a Cd of 0.767 which is far too low.

Does anyone have any ideas as to why my Cd are so far under what they should be? Other than nu in transport properties are there any other ways to specify the fluid properties like density that I'm missing?