[dinonettis]

Hi everybody,

I'm a new user of openfoam and I'm trying to analyse a naca profile with potentialfoam. Although I'm quite sure concerning the boundary conditions these are the results that I get on a C-grid:




The boundary conditions are the following:
-domain contour: freestream (U=239.6 m/s p=26624 Pa)
-lateral side:empty (2D analysis)
- wing: wall

and this is the 0/U file:

dimensions [0 1 -1 0 0 0 0];

internalField uniform (239.6 0 0);

boundaryField
{
defaultFaces
{
type empty;
}

lateral_side1
{
type empty;
}

lateral_side2
{
type empty;
}

outlet
{
type inletOutlet;
inletValue uniform (239.6 0 0);
value uniform (239.6 0 0);
}

wing
{
type fixedValue;
value uniform (0 0 0);
}

freestream
{
type inletOutlet;
inletValue uniform (239.6 0 0);
value uniform (239.6 0 0);
}
}


I hope somebody can help me.
Thank you very much

dino

[ngj]

Hi

I could not download your attached file, but anyway:
PotentialFoam solves the potential flow equations, but you are specifying a no-slip condition on the wing. This will include shear into the solution, which violate the assumption of irrotational flow.
Thus try to change the boundary condition at the wing to a "type slip" and see what happens.

Best regards and enjoy OF

- Niels

[dinonettis]

sorry but I did not realize the images did not appear on the forum. Anyway now I hope I'll be able to show you the results:

[dinonettis]

sorry but I did not realize the images did not appear on the forum. Anyway now I hope I'll be able to show you the results:

[dinonettis]

As you can see in the previous image it is strange that the velocity around the wing (and in the whole domain) is equal to 0, whilst it should be 239.6 m/s according to the boundary condition! Moreover there is only a little flow perturbation on the trailing edge, but the velovity increase very much inside that!!
Finally this is another view of the whole domain (C-grid) in terms of streamlines, quite strange as well:

[dinonettis]

hi niels,

I've just tried to follow your advice, substituting the wall with the slip condition on the wing. Unfortunately I get more or less the same results (both in terms of U range and streamlines). What do you think about that??

[ngj]

Hi Leonardo

Sorry for not answering before, but here in Denmark we have a nice think called "big-prayer day", which is a holiday. A king some years back was annoyed by all the religious holidays scattered all over the year, so they were collapsed into one.

It does look strange indeed. I took a closer look on your boundary conditions, and I am not sure if you are allowed to use empty in two dimensions when solving a 2-dimensional flow!?! I would set the upper and lower boundary to symmetryPlane.

You could try to test your setup on a more simple geometry, such as a cylinder and see if you get the correct analytical solution.

Best regards,

Niels

[darioth]

Hello Leonardo!

I am trying with potentialFoam with a 0015 and I have the same problem.

In the trailing edge, the velocity increase a little bit (like 70% than the free flow) but the rest of the flow field seem to be right, although this perturbation in the t.e. affects the values (not the distribution) of the velocity field.

Did you fix your problem?

Any tip will be usefull.

Best regards!!!