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April 8, 2009, 16:04 |
Outlet Problem
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#1 |
New Member
Faraaz
Join Date: Mar 2009
Posts: 11
Rep Power: 17 |
Hi everybody. I am simulating a flow around a body and am getting the error message below. I do not really understand why I am getting this error. Can anybody please help me understand that.
Thanks. Faraaz -------------------------------------------------------------------+ | ****** Notice ****** | | A wall has been placed at portion(s) of an OUTLET | | boundary condition (at 52.0% of the faces, 51.6% of the area) | | to prevent fluid from flowing into the domain. | | The boundary condition name is: Outlet. | | The fluid name is: Air at 25 C. | | If this situation persists, consider switching | | to an Opening type boundary condition instead. | +--------------------------------------------------------------------+ +--------------------------------------------------------------------+ | ERROR #001100279 has occurred in subroutine ErrAction. | | Message: | | Floating point exception: Overflow | | | | | | | | | | | +--------------------------------------------------------------------+ |
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April 8, 2009, 18:56 |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,703
Rep Power: 143 |
Hi,
The first message says you have reverse flow at that outlet. It is only a warning, this is not always a problem. The second is an overflow error, the simulation has diverged. Glenn Horrocks |
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April 9, 2009, 09:25 |
outlet problem
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#3 |
Senior Member
Bharath kumar
Join Date: Apr 2009
Posts: 169
Rep Power: 17 |
hi,
try this. first change the boundary condition to opening.then try. if it is not successful then check ur mesh quality.it may have negative elements. or use some coarse mesh.check ur boundary conditions too |
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April 9, 2009, 15:51 |
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#4 |
New Member
Faraaz
Join Date: Mar 2009
Posts: 11
Rep Power: 17 |
Hi,
Thanks guys for helping. Yes I am trying some stuff right now. If there's any problem, I will let you guys know. |
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April 10, 2009, 12:02 |
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#5 |
New Member
Michael
Join Date: Apr 2009
Posts: 20
Rep Power: 17 |
Hi all
I have the same problem but also two other questions. 1) How can I be sure that there will be no inflow in a opening as bc for outlet? 2) Also what would be the most "correct" way to define/assume the temperature at the outlet? I have used a subroutine to calculate the average temperature for my outlet region since i thougt this was smart to do. kind regards Michael |
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April 11, 2009, 08:47 |
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#6 |
Senior Member
Bharath kumar
Join Date: Apr 2009
Posts: 169
Rep Power: 17 |
hi,
1) check your areaave,massave variables at opening.if the deviation between variables are high then there may be inflow. 2) could u explain ur problem further more detail? |
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April 11, 2009, 08:59 |
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#7 | |
New Member
Michael
Join Date: Apr 2009
Posts: 20
Rep Power: 17 |
Quote:
The problem is that when I define a opening a temperature at the opening is nessecary. So by the subroutine the program calculate a average temperature for the region I have define as the outlet. I am in doubt if this is the right way to set the temperature or is I just could type in a given temperature? kind regards Michael |
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April 11, 2009, 11:15 |
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#8 |
Senior Member
Bharath kumar
Join Date: Apr 2009
Posts: 169
Rep Power: 17 |
you just set the opening temperature as an approximate guessed one.when solving the problem, solver will fix the temperature.
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April 15, 2009, 06:50 |
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#9 |
New Member
Tassi
Join Date: Mar 2009
Location: Mumbai, India
Posts: 11
Rep Power: 17 |
Hi Michael
Your method for defining the temperature at Opening is correct. Wall generation at Outlet can signify many things. See the CFX documentation on setting boundary conditions. BOL Tassi |
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April 15, 2009, 07:22 |
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#10 | |
New Member
Michael
Join Date: Apr 2009
Posts: 20
Rep Power: 17 |
Quote:
I think the reason why the solver creates artificial walls is caused by a recirculation zone. So i thougth that it would be appropriate to model the outlet as an opening to avoid numerical error caused be a wrong pressure field. I have added i screendump of my model where the inlets and outlet region is illustrated. The 3D blocks are persons. It is the region below the 3D blocks the recirculation zone is expected and here the solver creates artificial walls. Kind regards Michael |
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April 15, 2009, 21:04 |
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#11 |
Senior Member
Bharath kumar
Join Date: Apr 2009
Posts: 169
Rep Power: 17 |
hi Michael,
i have a doubt on the simulation. Even if you give the outlet as opening, whether the artificial wall created? |
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April 16, 2009, 00:27 |
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#12 |
New Member
Tassi
Join Date: Mar 2009
Location: Mumbai, India
Posts: 11
Rep Power: 17 |
Hi Michael
Yes the solver creates artificial wall cause of recerculation. You can deactivate solver from creating wall at boundaries by deactivating the function in expert parameters in Pre. Hasn't been of much help though. Normally I solve such problem by extending the outlet a little away from such recirculations. Sometimes adjusting mesh size and decreasing timesteps have helped. BOL Tassi |
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