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How important is clean geometry for CFD?

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Old   April 9, 2011, 18:03
Question How important is clean geometry for CFD?
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I am well aware of the importance of a clean topological model when it comes to performing FEA analyses, because the mesher really has a tough time with tiny faces and short edges and other such guck.

Since CFD has more of a grid approach to discretization, does it matter as much if your geometry is clean or not?

Does it also 'mesh' the model similar to finite elements or are finite difference/volume methods working entirely different? What about a solution that takes into account heat conduction in solids as well, what about then?
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Old   April 10, 2011, 01:48
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Quote:
Originally Posted by Kevin De Smet View Post
I am well aware of the importance of a clean topological model when it comes to performing FEA analyses, because the mesher really has a tough time with tiny faces and short edges and other such guck.

Since CFD has more of a grid approach to discretization, does it matter as much if your geometry is clean or not?

Does it also 'mesh' the model similar to finite elements or are finite difference/volume methods working entirely different? What about a solution that takes into account heat conduction in solids as well, what about then?
Yes it does matter a lot in CFD weather your geometry is clean or not. It wil have big problems since you create a very detailed volume mesh and if your geometry has some bad feature(small extrusions holes, non water tight geometries) you will not only have a tough time meshing, but also solving the simulations.
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Old   April 10, 2011, 09:48
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In my experience having a clean geometry is crucial. Without a clean geometry it is very difficult to obtain a quality mesh without some of the bad things that were mentioned in the post above.

Having those "bad things" can lead to divergence in your simulations, lack of proper convergence or poor results in those areas.
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Old   April 11, 2011, 19:05
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Bad geometry is a recipe for disaster in every way.

If you have bad geometry, chances are something got messed up somewhere and no one wants to take the time to fix it. It is frustrating, but it has to be done or else you'll shoot yourself trying to debug your mesh and solutions.

The question is, why WOULD you begin any type of simulation with corrupt geometry? If it's a time thing, then just be patient and fix it... you'll be better off in the end.
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Old   April 12, 2011, 13:28
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Glad to hear it, I'm a proponent of clean models myself. Not only for the repercussions a dirty model can have - just seeing nasty topology makes me just go crazy and I want to fix it! Whether it would make any deal or not.
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Old   April 13, 2011, 10:48
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Originally Posted by Kevin De Smet View Post
Glad to hear it, I'm a proponent of clean models myself. Not only for the repercussions a dirty model can have - just seeing nasty topology makes me just go crazy and I want to fix it! Whether it would make any deal or not.
i can tell you...it takes double the time or more to debug a volume mesh....so have it cleaned before that ! ! !
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Old   April 13, 2011, 10:52
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... why WOULD you begin any type of simulation with corrupt geometry? ...
Because it is the only thing available! Which leaves you the analyst in the position where you can clean it, wrap it, or recreate it. What works best is wholly problem dependent. Operator experience can pay serious dividends.

The other option is to throw your hands up & complain the CAD data is unusable. Since your customer likely won't want to recreate the CAD data, you run the risk of losing business to someone who will work through bad CAD data.
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Old   April 13, 2011, 20:44
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Because it is the only thing available! Which leaves you the analyst in the position where you can clean it, wrap it, or recreate it. What works best is wholly problem dependent. Operator experience can pay serious dividends.

The other option is to throw your hands up & complain the CAD data is unusable. Since your customer likely won't want to recreate the CAD data, you run the risk of losing business to someone who will work through bad CAD data.
Every analyst should have medium to high experience with CAD for this very reason. No reason to throw your hands up if the geometry is corrupt, just correct it and move on.
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