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July 5, 2012, 01:30 |
Fully Developed B.C. in CFX
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#1 |
Member
Hamed
Join Date: Oct 2009
Posts: 64
Rep Power: 16 |
Dear friends,
I am going to simulate fluid flow in a circular tube using CFX, at the outlet of the tubes "Fully developed" boundary condition should be used, in CFX what boundary condition is related to fully developed flow ? in fact in fluent there is an " outflow" B.C. but in CFX I do not know. Sincerely |
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July 5, 2012, 05:59 |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,819
Rep Power: 144 |
Use an outlet.
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July 5, 2012, 07:03 |
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#3 |
Member
Hamed
Join Date: Oct 2009
Posts: 64
Rep Power: 16 |
thank you but are you sure that "outlet" means fully developed condition ?
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July 5, 2012, 08:01 |
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#4 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,819
Rep Power: 144 |
Read the documentation for what an outlet means mathematically, but unfortunately I think you will find the description incomplete. By fully developed most people seem to think zero normal gradient. CFX takes a bit of a different approach and makes the boundary condition part of the solution variables, that is the boundary value for the other variables are convected/diffused from the domain.
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July 5, 2012, 12:56 |
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#5 |
Member
Hamed
Join Date: Oct 2009
Posts: 64
Rep Power: 16 |
thank you gorrocks , I read the documentation but I have another question, in the documentation speak just about velocity fully developed boundary condition, but do you know can impose the thermally fully developed boundary condition ?
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July 5, 2012, 18:37 |
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#6 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,819
Rep Power: 144 |
As discussed in the documentation, CFX uses the value convected from the domain as the thermal condition on an outlet boundary. This is different to a zero normal gradient boundary which some other codes use.
But in fully developed flow both approaches are equivalent. So to call the zero normal gradient approach a "fully developed flow boundary" and the CFX approach as something else is missing the point. |
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July 5, 2012, 21:25 |
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#7 |
Member
Hamed
Join Date: Oct 2009
Posts: 64
Rep Power: 16 |
Dear ghorrocks, thank you from your help and sorry for consuming your time, in fact I test what you have told but unfortunately there is not "zero gradient" item in the outlet boundary condition of a laminar flow, where is that?
Sincerely |
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July 6, 2012, 02:03 |
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#8 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,819
Rep Power: 144 |
CFX does not have an option with zero gradient at the outlet.
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