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Fluent convergence issues 2D airfoil

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Old   September 17, 2019, 23:44
Smile Fluent convergence issues 2D airfoil
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Ferruccio Rossi
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Hi all,

I am working on my thesis and I am starting by simulating flow over a 2D airfoil NACA 0012 in FLUENT. I can't get my simulation to converge properly (or at least, in my opinion it is not converging properly).

In MESHING, I am using a structured mesh with 233,000 elements (see pics). I tried to get the elements to become finer as they get closer to the airfoil through element biasing.

In FLUENT, I am using the following parameters:
- Pressure based solver
- Laminar model (since my airfoil chord is 25 cm and thus low Re)
- Air with constant density
- Velocity Inlet BC (20 m/s)
- 0 angle of attack
- Pressure outlet for the rest of the domain (top, bottom, and back).

I am not understanding why my plots look so off. The residuals are oscillating greatly and are not converging. On the other hand, the mass flow and drag plots seem to be mostly steady, except for a spike which is completely out of the expected range, which makes me think that these plots are not reliable.

Also, I am getting reversed flow on one of the faces of the pressure outlet (not sure if this impacts the results or not).

Do you guys know what I might be doing wrong? I think all my selections make sense and I don't understand what I might be doing wrong.

Note: I also tried an unstructured mesh with quads and inflation layers, but I still got similarly strange plots...

Any help is greatly appreciated!
Thank you guys
Attached Images
File Type: jpg Mesh.JPG (44.5 KB, 18 views)
File Type: jpg Mesh airfoil.jpg (143.1 KB, 17 views)
File Type: jpg Residuals.JPG (87.2 KB, 13 views)
File Type: jpg drag.JPG (48.7 KB, 11 views)
File Type: jpg Mass flow.JPG (49.0 KB, 11 views)
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convergence, fluent, mesh, plot, residuals

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