[mortazavi]

Hi,
i am silumating fsi of a 3D hydrofoil at high Re numbers.
The simulation is unsteady, however i only look at the staedy-state final results.
the simulation converges to 2e-4 but the issue is that the final solution is on a low-quality mesh because of the deformation of hydrofoil.
The picture is attached to post.
Any idea to avoid low-quality final mesh???thanks

[ghorrocks]

First thing to try is to adjust the mesh smoothing parameters in the moving mesh options.

Then check the mesh smoothing equations are accurately resolved - try tightening the mesh smoothing convergence tolerance.

If that does not work you might need to consider dynamic remeshing.

[mortazavi]

Dear ghorrocks, thanks for your helpful comment.
for the first and second comments i have found enough documents.
could you please intoduce me a good reference or tutorial for dynamic remeshing? cfx help is not helping me.

Originally Posted by ghorrocks

First thing to try is to adjust the mesh smoothing parameters in the moving mesh options.

Then check the mesh smoothing equations are accurately resolved - try tightening the mesh smoothing convergence tolerance.

If that does not work you might need to consider dynamic remeshing.

[ghorrocks]

There are examples on dynamic remeshing in ICEM on the ANSYS customer webpage.

[mortazavi]

Hi ghorrocks,
Is dynamic remeshing supported with fsi in workbench?

Originally Posted by ghorrocks

There are examples on dynamic remeshing in ICEM on the ANSYS customer webpage.

[ghorrocks]

I am not sure, you will have to check. But I suspect you can do it.

[mortazavi]

hi ghorrocks,
remeshing is not applicable for fsi with cfx.
Another question; do you think if with using domain interface i can get rid of low quality mesh under the hydrofoil as depicted in this picture?
i mean a very fine mesh near the hydrofoil for the boundary layer elements and wake region, and coarser mesh far. in this case i can use stiffness increase near small volumes without any issues.
thanks

Originally Posted by ghorrocks

I am not sure, you will have to check. But I suspect you can do it.

[ghorrocks]

Yes, using GGIs can help.

Some other comments:
* The mesh smoother should not do what you show when it is adjusted properly. Are you sure the mesh smoothing convergence tolerance is tight enough?
* Your mesh is also not ideal as you have high aspect ratio elements in the bulk flow. If you improved your mesh such that the high aspect ratio elements were only in the foil boundary layer that would improve things and probably help the mesh smoother as well.

[mortazavi]

Hi ghhorocks,
As you can see in the attached photo, my main issue now is in the wake region. so according to my supervisor's reccomendation, what i have to do is to define a CEL for the stiffness (increase near small vol). For now the exponent is a constant value. the foil moves up while the small volume elements in the wake region are stiff enough to stay in their initial position and don't move. So I have to decrese the exponent for X> X(TE).
for example exponent=0.2 but for X>X(TE) exponent=0.01.
Any idea please?
If you agree can you guide me to write this CEL?
thanks

[ghorrocks]

What version of CFX are you using? Recent versions of CFX have much more options here than older versions.

I would have thought that simply increasing the mesh stiffness diffusion value in proximity of the foil would be best. This is a GUI option in recent versions of CFX.

And by the way: rapid changes in stiffness like you suggest are a bad idea because the mesh at the interface gets highly distorted. You need to gently ramp between values to avoid this.

[mortazavi]

ghorrocks Thanks,

I am using version 16. Could you please explain more about GUI option in your previous post?
by the way, as in the attached file, according to your recommendation i have created multiple zone in the foil and wake region to be able to define different stiffness for different domains. is that acceptable you think?
regards,

[ghorrocks]

Yes, your regions should help. But still you will have to be careful about the transitions.

I am on holidays and away from my workstation so cannot look up the new options in current CFX versions for you.