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solution problem : A wall has been placed at portion(s) of an OUTLET

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Old   August 8, 2010, 08:20
Default solution problem : A wall has been placed at portion(s) of an OUTLET
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i'm dowing a small analysis on CFX, i'm getting unlogical results, and while running the solver, i see this message with each Iteration :
| ****** Notice ****** |
| A wall has been placed at portion(s) of an OUTLET |
| boundary condition (at 35.2% of the faces, 8.6% of the area) |
| to prevent fluid from flowing into the domain. |
| The boundary condition name is: Outlet. |
| The fluid name is: Air Ideal Gas. |
| If this situation persists, consider switching |
| to an Opening type boundary condition instead. |
the inlet condition is Normal Speed = 150m/s
total temperature 300K

the outlet condition : relative pressure : 0kPa

any opinion ?
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Old   August 8, 2010, 18:46
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Glenn Horrocks
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I really should this answer up as a FAQ, it has been asked thousands of times. Do a search of the forum and you will find lots of questions on it. Also the CFX documentation discusses it.

It merely says that you have backflow at an outlet and this is not allowed. To stop it the solver has created artificial walls at the outlet to stop the backflow. Whether this is acceptable or not depends on your problem, but in general it is best avoided. The best fix is usually to move the outlet further downstream to where the flow is fully in one direction.
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