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Poor surface resolution caused by volume shapes

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Old   September 23, 2011, 06:34
Default Poor surface resolution caused by volume shapes
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Hi,

I am a beginner to CFD and StarCCM+

Currently I am trying to simulate the flow around an airfoil.
I use the "trimmer" and "prism layers" around the airfoil for meshing.
When I just create a mesh with refinement close to the airfoil structure the mesh is just fine.

But, when I define a "volume shape" (block) in order to create a finer mesh around the trailing edge, for example, StarCCM+ kind of destroys the geometry of the airfoil.
The round parts of the geometry get approximated roughly by secants. That results, when a simulation is applied, in pressure jumps at the so generated edges.

Can anyone tell me, why this happens? I just included this one "volume shape" and stick to the other settings. Is there a way to force StarCCM+ to follow the exact geometry, when "volume shapes" are applied?

Any help would be much appreciated.

Philipp
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Old   September 26, 2011, 16:21
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Can you please post a picture of the destroyed surface? Do you set mesh values on boundaries while using the volumetric control? What values do you set in the VC and on the boundaries? What file type do you use for import? Working on parts level or regions level?

Usually CCM+ doesn't destroy a geometry just because it's Monday. There has to be a specific reason, and is has to do something with your settings, as my airfoil simulations usually went fine.
Give us more input, so we get a chance to help you.

Cheers
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Old   September 26, 2011, 17:08
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Is it messed up at Surface mesh level or just Volume mesh?


If it is bad at surface mesh level, I have found turning off CAD Projection in the mesh continuum and turning off Retain Geometric Features in the Surface Mesh Solver Setttings can help sometimes. Strange as both those options sound like they should be truer to CAD...
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Old   September 28, 2011, 05:39
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Hi,

thanks for the replies.

I just tried to mesh with cad-projection and retrained geometry features turned off but the result remained the same.
The surface and the volume mesh both do not represent the exact geometry.

The prism layers and the surface size of the mesh are defined in the regions node.

In the volumetric control I just customized the trimmer settings.

I attached 2 pictures to show you the difference between the surface with and without a volumetric control.

I did not import any file to create the surface. I had a list of points that I imported into StarCCM+'s geometry tool. These points were connected by a spline.
Attached Files
File Type: pdf surface_with_vc.pdf (87.6 KB, 33 views)
File Type: pdf surface_without_vc.pdf (85.1 KB, 26 views)
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airfoil, geometry, mesh, secants, volume shape

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