Dynamic mesh fidelity
 

I've been doing simulations of oscillating airfoils in Fluent using dynamic meshing. I usually use spring-based smoothing with a spring constant of 0 and local remeshing with as fine parameters as possible. However, the grid fidelity around the airfoil tends to degrade rather quickly using these techniques, no matter how fine I try to set the remeshing parameters.

Are there any suggestions for getting a better moving grid near the airfoil? For example, it would be nice if I could set up a boundary layer grid in Gambit and set that as the moving zone (with the airfoil, of course). I know I could do this if I made a separate wall to define the zone around the airfoil, but of course, I wouldn't want it to be a real wall. Are there any suggestions in dealing with this?

Thanks,
Dan

in Gambit create a volume surrounding your airfoil and define it as separated fluid domain.
In fluent set the rigid body motion on your airfoil AND also on this fluid domain

Thank you! I saw another similar thread where you suggested something like that, but I wasn't quite clear what you meant. I will try this today.

Wow, it actually worked on the first try. Thanks again, mAx.

Some more details for anyone else trying to do this:
-Set the boundary type of your interface to "interior."
-Apply dynamic mesh motion to the real surface, the interior boundary, and the fluid domain between them.

Hi Dan
I would like to ask you a question.I have tried a similar simulation with an oscillating cylinder in 2D.The mesh was built with ICEM.
I've used the same tips(real boundary-interior and the interior boundary all moving with rigid motion),but when i look to the boundary layer i found inertial effects e.g. in the first cell of boundary layer the vector of velocity is not parallel to the surface but have a vertical component.

Did you noticed this effect or do you think that i've mede some mistake?

Thanks in advice

Paul

Paul,

Are you sure the normal component of velocity is incorrect? In a viscous flow there should be some normal component in the boundary layer due to the rotational nature.

Dan

In fact i'm not sure...i don't have a lot of CFD experience,but the fact that the viscous sub layer have a normal component it sounds me strange,flow shoud be tangential to the surface ...
Maybe is my mistake...
Thanks for your answer

I should probably clarify what I said. It depends on what your motion is and where you are looking. If you have separated regions, I would expect to see normal components of velocity there. If you're not looking at a separated region it should be fairly tangential and the boundary layer should be thin.

Hi all,

is not creating a volume sourranding my body similar using sliding mesh? is not different using sliding or deforming meshes?