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#1 |
New Member
Harish Abubaker
Join Date: Jun 2013
Posts: 6
Rep Power: 13 ![]() |
I came across a statement that use of zero gradient boundary conditions for LES and DNS would result in unphysical results.
Can anyone please explain why. |
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#2 |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,813
Rep Power: 73 ![]() ![]() ![]() |
zero gradient BC can be adopted for outflow provided that is fixed far from the main zone... it can be improved by higher approximations
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#3 |
New Member
Harish Abubaker
Join Date: Jun 2013
Posts: 6
Rep Power: 13 ![]() |
Thank you..but can you also explain why does this happen ?
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#4 |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,813
Rep Power: 73 ![]() ![]() ![]() |
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#5 |
New Member
Harish Abubaker
Join Date: Jun 2013
Posts: 6
Rep Power: 13 ![]() |
Had to ask one more thing, why is it then ok to use the zero gradient bc for RANS ?
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#6 |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,813
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#7 | |
Senior Member
Join Date: Aug 2011
Posts: 272
Rep Power: 15 ![]() |
Quote:
dphy/dt + U*dphy/dn=0 (derivatives here are partial derivatives and U is a velocity which may be defined by different means, (it can be the mean velocity for example). phy stands for each componnent of the velocity vector. |
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#8 |
New Member
Harish Abubaker
Join Date: Jun 2013
Posts: 6
Rep Power: 13 ![]() |
Thank you very much guys. I get the idea.
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#9 |
New Member
The Beginner
Join Date: May 2014
Posts: 1
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How can i put Orlanksy boundary condition in FLUENT ?
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#10 |
Senior Member
Jianrui Zeng
Join Date: May 2018
Location: China
Posts: 157
Rep Power: 8 ![]() |
Does someone know the Orlansky boundary condition or convective boundary condition in Openfoam? I want use this boundary in DNS simulation. Thank you.
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#11 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
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#12 |
Senior Member
Join Date: Dec 2017
Posts: 153
Rep Power: 8 ![]() |
Yes. it is called "advective" in openFoam and does:
du/dt + Udu/dn=0, at the outflow boundary. For more theoretical aspects on this condition you can look at ferzinger and peric book, chapter 9. |
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#13 |
Senior Member
Jianrui Zeng
Join Date: May 2018
Location: China
Posts: 157
Rep Power: 8 ![]() |
Thanks to AliE and LuckyTran ! I will have a try later!
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