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In what case will GGI bring the accurate results for unmatched nodes? |
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July 24, 2012, 06:09 |
In what case will GGI bring the accurate results for unmatched nodes?
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#1 |
Senior Member
lnk
Join Date: Feb 2011
Location: Switzerland
Posts: 118
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Hi, everyone.
Thanks for your time to look at this question. I'm thinking about using GGI for the unmatched nodes interface between fluid-fluid domain for my case. May I ask in what case will GGI bring accurate results? ( I searched for this at the tutorial but didn't find any answer. ) Best regards and many thanks again, lnk |
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July 24, 2012, 19:33 |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,703
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Yes, GGIs are quite accurate. It is very unusual for a GGI to introduce enough error into a simulation to be a problem.
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July 25, 2012, 02:19 |
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#3 | |
Senior Member
lnk
Join Date: Feb 2011
Location: Switzerland
Posts: 118
Rep Power: 15 |
Quote:
http://www.cfd-online.com/Forums/ans...eration-2.html |
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July 25, 2012, 02:26 |
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#4 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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You should compare this to a known accurate or analytical answer. If it has some distortion adjacent to the interface but is accurate away from it then that is fine for most users. Also I think you will find the distortion is amplified by the way the contours are drawn in CFD-Post.
So "low accuracy" is dependant on what you are looking for accuracy in. If you need it to get the correct pressure drop across something you will almost certainly find it OK. If you need smooth temperature contours in a CHT body then it might not be so appropriate. But sweeping comments like "GGIs are low accuracy" are not helpful. But there are cases when they will cause problems. |
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July 25, 2012, 04:32 |
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#5 |
Super Moderator
Alex
Join Date: Jun 2012
Location: Germany
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I posted this comment in the context of a tedious hexa-mesh generation in a difficult geometry.
I just thought it would be a pity to spend several days creating a block-stuctured mesh and then using an interface to sew together non-matching parts of the mesh. |
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July 25, 2012, 12:14 |
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#6 | |
Senior Member
lnk
Join Date: Feb 2011
Location: Switzerland
Posts: 118
Rep Power: 15 |
Quote:
So if I'm only looking for pressure drop, I can always use GGI without considering the inaccuracy it might bring. Right? |
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July 25, 2012, 18:42 |
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#7 | |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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Quote:
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August 2, 2012, 10:06 |
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#8 |
New Member
Join Date: Jul 2012
Location: Germany
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Hi
my advice is to always use different ways to analyze your results. also create monitor points through different expressions and check if they change over time(steady state sim) ... (sometimes i get gigantic pressuredrop fluctuations over my fluid-domain when i evaluate with massFlowAve()@REGION:... - even if the end result via massFlowAve()@Plane is very plausible) |
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August 2, 2012, 20:28 |
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#9 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,703
Rep Power: 143 |
It is always best to test things you are suspicious of for accuracy in your case. So I would compare a GGI simulation versus one without the GGI and see if the accuracy is acceptable. If generating the non-GGI mesh is impossible (that is why you put the GGI in there in the first place ) then dream up a simple little test case which uses the same physics and fundamental flow, but is simple enough to run with and without the GGI. If the GGI is acceptable in the simple test case then it will be OK for the real simulation.
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