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[ANSYS Meshing] CutCell Mesh & Inflation

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Old   July 12, 2012, 09:26
Default CutCell Mesh & Inflation
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Çağlar Coşkun
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Hello
I am trying to do a simulate the natural convection in a cavity, having a complex geometry. I used the new Cut Cell method to mesh the geometry. I need to use inflation layers to resolve the thermal boundary layers better.
When I add the inflation layers, they create stair-stepping at various locations, and results a bad quality mesh. This causes convergence problems in Fluent.
I decreased the stair stepping problem by adjusting advanced inflation settings, but couldn't prevent it.
Any ideas?
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Old   July 12, 2012, 15:22
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Sijal Ahmed Memon (turboenginner@gmail.com)
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cant u try ICEM?
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Old   July 12, 2012, 15:33
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I don't know how to use icem. Should I try? Is it better at handling complex geometries?
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Old   July 12, 2012, 15:36
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Rule of thumb: For simple geometries use Ansys meshing and for complex cases use ICEM CFD.

ICEM CFD is very good at handling complex geometries. You should try it and you can also get very good help at this forum from experts including The Simon .
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Old   July 13, 2012, 08:56
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Cutcel is really in a separate category within ANSYS Meshing, it should be able to handle your complex geometry (it was designed for automotive underhood which is as complicated as it gets).

Are you using version 14? There was a lot of work on Cutcel prism between 13.0 and 14.0 and I noticed it got a lot better at handling these things.

Maybe post a picture so we can see what you mean. Typically, the mesher only allows prism stair stepping when you set your physics to CFD => CFX, so check that setting also.
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Old   July 14, 2012, 08:44
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Far and PSYMN, thanks for replies!
Here are some pictures of my mesh. In fact, in most parts of the geometry, there is no stair stepping. Instead of that, layers are compressed a lot.
http://postimage.org/gallery/123kqsxo/
My min. mesh size is 4mm, and number of inflation layers is 5.
PSYMN, it is not possible to change physics or solver preference if cutcell is active, as seen on pictures.
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Old   July 16, 2012, 16:52
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I asked around in development for you and was told that they had a name for this (they called it the "corner shrink bug") and that it was sorted out back in May (therefore fixed in R14.5).

In the mean time,
Quote:
reduce gapfactor to 0.5...
Keeping Height over base below 0.5 is also recommended.
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Old   July 16, 2012, 17:12
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Quote:
Originally Posted by PSYMN View Post
reduce gapfactor to 0.5...
ah.. the gap factor is 2 in my mesh is it better to reduce it? I made it 2 because, in tutorials, it is written that increasing this value makes the inflation layers more compressed, thus reducing the stair stepping.

The other inflation parameters are as follows:
max. height over base: 0.5
max. angle: 180
fillet ratio: 0.5
fix first layer: no
inflation type: smooth transition

What can you suggest about these settings?

Thanks a lot for your help...

Last edited by CaglarCoskun; July 16, 2012 at 17:30.
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Old   July 16, 2012, 17:32
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Give it a try and tell us if it works...

I am not so expert at this (yet) that I can diagnose it remotely.
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