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Old   January 8, 2011, 12:12
Default Dynamic mesh fidelity
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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
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Old   January 10, 2011, 02:34
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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
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Old   January 10, 2011, 10:48
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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.
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Old   January 10, 2011, 16:37
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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.
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Old   January 13, 2011, 11:52
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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
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Old   January 13, 2011, 13:34
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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
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Old   January 13, 2011, 17:21
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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
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Old   January 13, 2011, 18:07
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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.
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Old   March 19, 2011, 09:01
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Hi all,

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