[hakonbar]

Hi everyone!

My name is Håkon Line, and I'm a mechanical engineering student at the NTNU, Trondheim. I started using OpenFOAM about half a year ago, and am now using it for my Master's thesis. I'm posting here because I've recently hit upon a problem which at first I thought would be trivial, but which has me completely stumped. Any help would be immensely appreciated, as I still have a long way to go and my deadline is fast approaching =)

I'm simulating a classical benchmark case, the naca0012 foil at Ma = 0.15, Re = 6*10⁶ (http://turbmodels.larc.nasa.gov/naca0012_val.html). I'm using simpleFoam with the SA-model and 2nd order upwind convection schemes. The mesh is generated with SHM. The airfoil is generated from the equation given at the previously linked-to webpage, and converted to stl-format by the utility "points2stl" developed by Alejandro Roger.

Now, my problem is that the forces on the wing, as calculated by the utilities in 'libforces.so' are way too low:
(Cl = 0, 0.104 and 0.193 for alpha = 0, 5 and 10 degrees, respectively)
(Cd = 0.0019, 0.0023 and 0.0041 for alpha = 0, 5 and 10 degrees, respectively)

As these values are several times smaller than they should be, I suspect a multiplying factor is off somewhere, but I've no idea where that may be. The values for the lift and drag coefficients are consistent with the forces reported in forces.dat, so the error doesn't lie with the non-dimensionalization.

Furthermore, when I retrieve the surface normals and the surface pressure from paraView, and use that to find the pressure distribution and lift on the wing, my results closely match the validation data.

Since my pressure distribution is ok, I guess I could ignore the bad data produced by libforces, but I'm going to simulate this and similar shapes in pimpleDyMFoam, and I want to make sure that the forces "seen" by the wing are correct before I proceed. Where should I start looking?

best regards,
Håkon Line

I'm attaching a dropbox-link to one of my run cases:

http://dl.dropbox.com/u/21618777/12a10simpleSA.zip