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LES of vortex rope in the elbow draft tube

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Old   March 22, 2017, 23:09
Default LES of vortex rope in the elbow draft tube
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LintaoZhong
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Hi guys
I am trying to predict and analyze vortex rope in the elbow draft tube by means of CFX. I read some literature and follow the guides in ANSYS Help about Large eddy simulation, but there are some issues happened to me. I can't sure whether it's error settings in CFX or bad initial conditions. So I need everyone's help.
(1) Should I choose DES rather than LES for analyzing vortex rope? I noticed that the difference between LES and DES is adjacent wall resolves, one use DNS and other use URANS. Main flow play a important roles in vortex rope, so whether I shouldn't spent so many time to resolve wall regions used LES.
(2) What's reason causing my residual surge like below figures, time step, the size of mesh or anything else? As below figure shows, residual is fastly convergence at first steady caculation and then, at transient caculations, it occurs so peaks with the increasing of residual. Is it correctly?
Lintao
In addition. are there anyone could give me one tutorial about LES in CFX. I don't sure whether my CFX settings is correct. Thank you very much
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Last edited by Sergeyevichsky; March 23, 2017 at 02:12. Reason: upload figures
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Old   March 23, 2017, 00:24
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Glenn Horrocks
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DES is used for flows off bluff bodies. LES is used in general turbulent flows - so I think you will not be able to use DES. But check the theory behind it to confirm this.

You are correct, it is likely the detailed wall effects are not important in your flow. This will make the model easier.

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Old   March 23, 2017, 01:48
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Quote:
Originally Posted by ghorrocks View Post
DES is used for flows off bluff bodies. LES is used in general turbulent flows - so I think you will not be able to use DES. But check the theory behind it to confirm this.

You are correct, it is likely the detailed wall effects are not important in your flow. This will make the model easier.

Can't upload figures? FAQ: https://www.cfd-online.com/Wiki/Ansy...n_the_forum.3F
Thank you very much. You gives me a new ideals about my study
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Old   March 23, 2017, 05:45
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There is LOTS of literature on using LES to model vortex flows in industrial cyclones. This has very similar physics to what you are talking about. So I would do some literature study before you start, and you should find lots of relevant stuff on industrial cyclones.
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Old   March 24, 2017, 04:50
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Quote:
Originally Posted by ghorrocks View Post
There is LOTS of literature on using LES to model vortex flows in industrial cyclones. This has very similar physics to what you are talking about. So I would do some literature study before you start, and you should find lots of relevant stuff on industrial cyclones.
Thanking for your suggestion.
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