[Varoesp98]

Hello, I am analyzing in Ansys Fluent a Naca 0012 for obtaining the lift and drag coefficient. I am using a triangular unstructured mesh, and I have created for the domain a rectangle around the airfoil. When I calculate everything I get on the results negative drag coefficient when I change the angle of attack to menos 20 for example. The angle of attack is changed in the x and y component inside the inlet as I have learned. If anyone can help me please contact me as soon as possible.
Thank you very much

[vinerm]

There are two important things to be taken care of for the reporting of coefficients - appropriate reference values in Reference Values panel and correct specification of direction of the force in which momentum is desired. If these are wrong, then coefficients will be wrong as well. Do note that this does not mean the simulation is wrong since coefficients are just post-processed from computed fields.

[Varoesp98]

Hello vinerm thanks for replying. In the geometry I used rotate and I have parameterized the analysis for obtaining all the results for different angles of attack (-20°,-15°, -10°, -5°, 0°, 3°, 5°, 8°, 10°, 12°, 15° and 20°). Also in the setup inside the inlet I used magnitude normal to boundary due to the reason that the airfoil is changing with the angle of attack so I want the velocity to be straight so the results are optimum ( I think I have xplained myself if not please tell me), but when obtaining the results, they are not completely correct. Is there anyway you can help to solve this? Can I share the ansys in the forum or do you know what can I do?
Thank you very much

[vinerm]

If you are rotating the foil for each case, then you will also have to rotate the direction for drag and lift. For each AoA, direction vectors for drag and lift have to be (cos AoA sin AoA) and (sin AoA cos AoA).

[Varoesp98]

Yes, I have also done but still it does not make sense the results.
Regards

[vinerm]

Check the reference values you have provided in the Fluent as well. If those are also correct, then there could be issue with mesh resolution or convergence. At higher AoA, there could be flow separation and finer mesh would be required. However, first you should check for results of 0 or low AoA. If even those are incorrect, then there is something wrong with your setup.

[Varoesp98]

Okey everything is done, but regarding to the part you are saying that first of all I must do the AoA of 0 and negative ones, is that very important? Because with the parametrization each of the AoA where donde individually but one after the other

[vinerm]

Until and unless you have a stable model, you should not use it for parametric study. In case one setup is wrong, you will end up having all cases wrong. A single case takes much less time than all the cases.

[Varoesp98]

Thank you very much vinrem, but I tried everything and it still does not work but thank you for the effort
Best regards and thank you very much