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Incorrect lift force in simpleFoam airfoil simulation

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Old   May 14, 2019, 17:11
Default Incorrect lift force in simpleFoam airfoil simulation
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Olov Danielson
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Hi!

I'm trying to simulate a symmetric NACA-0015 airfoil in 3d using simpleFoam in order to derive forces acting on it.

At 18 degree angle towards wind the results look about right
(+25% for drag force and -25% for lift force) compared to tabular values.
But at 0 degree angle I get roughly equal lift and drag force (lift is Y and drag Z) while I expected to have no lift force at all.

"""
SIMPLE solution converged in 6.95 iterations

forces forces_on_object write:
sum of forces:
pressure : (-0.00244928 -10.9063 -9.32257)
viscous : (1.46895e-05 -0.00138044 -3.18357)
porous : (0 0 0)
"""

Pressure and velocity seem to be equal above and below the profile (see attached images).

Any pointer to what I might have missed is much appreciated!

Thanks,
Olov
Attached Images
File Type: png pressure_screenshot.png (72.4 KB, 12 views)
File Type: png velocity_screenshot.png (70.4 KB, 11 views)
Attached Files
File Type: gz log.txt.gz (23.3 KB, 0 views)
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Old   May 18, 2019, 06:47
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Hi Olov, your mesh is not good enough. First, mesh needs to much finer. Second, boundary layer mesh is needed. Finally, you better use hex-dominate mesh. Also what turbulence model are you using?
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Old   May 18, 2019, 07:51
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Olov Danielson
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Hi Hokhay!

Thanks for your reply, I'm using kEpsilon RAS and I use snappyHexmesh to generate the mesh. I'll try your suggestions and get back with the results.


"""
simulationType RAS;

RAS
{
RASModel kEpsilon;
turbulence on;
printCoeffs on;
}
"""
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Tags
airfoil 3d, force, incorrect, lift and drag calculation, simplefoam

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