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Old   November 30, 2011, 05:22
Default Trailing edge difference
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oscar
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Hi there!

I got stuck with a problem in my CFX simulation. I'm trying to simulate the water flow around a truncated NACA0009 with no cavitation conditions. It should be a quite simple one but when I plot Cp vs chord the trailing edge zone does not give good results. I really don't know what is happening as the mesh seems ok and its density should be far more than enough.
Any suggestions?????
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Old   November 30, 2011, 06:02
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Glenn Horrocks
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Why do you say "the mesh seems OK"? How do you know? It is a very common beginner mistake to just assume that the super-fine mesh you spent has to be OK because.... it just looks fine.

Unless you have actually checked it is OK by a sensitivity analysis then you have no idea whether it is fine enough.

Sounds like you need to read this FAQ:
http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F
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Old   November 30, 2011, 06:10
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oscar
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"seems" OK, from a structural point of view, since no quality, skewness, aspect ratio...problem arise at ICEM and CFX also gives OK in its 3 fields of meshing check. You're right that there is no sensitivity analysis perform but, how could I if my starting point is so far from the real results.
The mesh density is far more than enough since I compare the results with empirical tests and with a CFD analysis performed by an author. This mesh - I have a picture of it- is coarser than mine.
Hope it is clearer.
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Old   November 30, 2011, 06:21
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Different solvers need different mesh densities to achieve accuracy. Do not assume that somebody else's mesh is OK for you without checking.

Have you looked at the FAQ? It lists the checks you should do when your simulation is not accurate.
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Old   November 30, 2011, 06:35
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oscar
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I'll check FAQ...
thanks
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