[dinonettis]

Dear all,

I'm trying to obtain the lift coefficient by means of the library forces.so (set in the ControlDict). The settings are the follwing:

-----------------------------------------------------
forces
{
type forces;
functionObjectLibs ("libforces.so");
patches (front_wing rear_wing main_wing);
rhoName rhoInf;
rhoInf 1.176;
CofR (0 0 0);
outputControl timeStep;
outputInterval 100;

}
forceCoeffs
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
patches (front_wing rear_wing main_wing);
rhoName rhoInf;
rhoInf 1.176;
CofR (0 0 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 0);
magUInf 7;
lRef 6.0;
Aref 1.0;
outputControl timeStep;
outputInterval 100;
}
--------------------------------------------------

As it is possible to see the geometry is composed by 3 profiles. Therefore the reference lenght I imposed corresponds to the global lenght (or chord) of the 3 profiles in the wind direction.
The result of the firts 1000 iteration (in which the simulation should be converged) is the following:

# Time Cd Cl Cm
100 0.0121195 0.0343389 0
200 0.0114814 0.0389873 0
300 0.0113282 0.0410893 0
400 0.01112 0.0436375 0
500 0.0108316 0.0464789 0
600 0.0105124 0.0490456 0
700 0.0102129 0.0515734 0
800 0.00987898 0.0542187 0
900 0.0094987 0.0563448 0
1000 0.00913385 0.0579033 0

First of all the coefficient seems to be still incresing with time, although the simulation should be converged (residuals 1e-7). However I don't think it will never reach the expected value that is around 3.
Which could be the reason of such a low value??

I'm using a k-epsilon model with wall functions and simpleFoam solver. Unfortunately I've just checked the y+ and it is exactly in the range in which it should not be, i.e. between 5 and 30.
So I have 2 question:
- such a big error could be due to the wrong y+??
- since I guess I have to modify the mesh, it is better to adopt a low Re model (I would prefer to avoid that due to the more complex mesh) or again wall functions??
Thanks you very much in advance.

Dino