[macbeth]

Hi,

I have read in some of the posts here that there could be a problem with the calculation of integral forces when using SRF (single reference frame) solvers.
It was said here somewhere that the torque e.g. on windmills is way too high.

Being quite new to OpenFOAM, I set up a case for a wind turbine and after some time got it working. I used the "forces"-function in the controldict and instantly ran into the same problem.

To bring some light into that case, I used paraview to compute the forces acting upon the surface of the blades.
(Quite tricky: extract block, generate normals, multiply p with normals, integrate values... et voila: Forces in X,Y,Z-directions.
For the torque we need to use the cross-product of (p*normals) and the coordinate-vector. Integration of that gives the moments.)

Now, if i compare this to the values I get from the forces-function, values are about 20% lower. Much more like I would expect them to be. So is the post-processing in OF damaged? Or maybe it doen't like simpleSRFFoam??

Does anybody else have similar experience?

Next question on my heart is the bc for a freestream around a wind turbine...

I tried to use a "slip" condition and was surprised that there seemed to be a boundary layer (at least looking at Uabs). can anybody suggest which bcs to use? Do I need something special for SRF? I have a cylindrical area around the blades, 2D upstream and 10D downstream.

Thx!
macbeth