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reversed flow on faces limited in 643 cells in region out

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Old   September 19, 2009, 06:10
Default reversed flow on faces limited in 643 cells in region out
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Hello everybody,
i am a newby and i dont know if introducing myself somewhere is required.
Anyway i am 27years old marine engineer from italy approaching for the first time on cfd planet.
I am asking for your help because any boat model i am trying to validate with cfd,return a message reporting what stated in the title of this thread "reversed flow on faces limited in 643 cells in region out"...
I tryed to change volume control dimensions up to 2,5 time boat length,width and depth...but the message won't disappear....although performing grid parameters of my multiphase.

So now i am trying with a second order solver...and the number of faces affected seem to get smaller iteration by iteration.
Can anyone explain me what's the meaning of the above mentioned message and what's the smartest solution to fix similiar problems without affecting solution and its transient?

i used velocity inlet and pressure outlet

Many thanks in advance

Last edited by emanuele; September 19, 2009 at 06:29.
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Old   September 21, 2009, 11:22
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Check your conditions on the outlet boundary.
Sometimes it's normal because the flow reserves before it gets a straight flow.
When I use a Pressure Outlet as a Inlet I get this on every iteration
To check the direction I use vectors on the boundarys.
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Old   September 21, 2009, 11:29
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Quote:
Originally Posted by Maddin View Post
Check your conditions on the outlet boundary.
Sometimes it's normal because the flow reserves before it gets a straight flow.
When I use a Pressure Outlet as a Inlet I get this on every iteration
To check the direction I use vectors on the boundarys.
Thank you for your support....but i imagine reversed flow could affect convergence!isn't it?
I would like to try a polyedral mesh in order to check if multifaces volumes can manage turbulent flow in a most accurate way...actually i m going with trimmer and its refinement on free surface..
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Old   September 21, 2009, 12:26
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Is your problem 2D or 3D?
When this is a 2D problem then your region is wrong.
Show more pictures!
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Old   September 21, 2009, 13:58
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my problem is a 3d problem and it don't wanto to converge!!I checked several times what should be wrong but i discovered nothing....
i performed mesh diagnostics and everything seems to be ok,i enlarged my continuum but nothing....solution keep going in a wrong way.I'll show more pic as soon as i can!
i performed some trials without degrees of freedom in order to be sure it is not a prblem related to initial condition an moments of inertia...but it's the same..
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Old   September 21, 2009, 15:20
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What settings to you use? Wall treatment? y+?
Bring more facts plz
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Old   September 22, 2009, 10:19
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ok,at the link below you can find my summary report ...
thank you for your big interest!!

http://www.megafileupload.com/en/fil...umem-html.html
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Old   September 22, 2009, 10:50
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Look at your courant number, maybe you have so choice a smaller time step.
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Old   September 22, 2009, 11:31
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Quote:
Originally Posted by Maddin View Post
Look at your courant number, maybe you have so choice a smaller time step.
thank you!!i will manage to optimize it!
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Old   September 22, 2009, 11:39
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Tell me when it works, picture looks very nice. Could be a really nice animation
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Old   September 25, 2009, 05:27
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ok...error found...i was using velocity modulus..At inlet flow direction is "inlet to outlet"...and you do not need to specify it using "-" or "+"...just use modulus of velocity
In continum you should specify everytime the direction of the flow....i was using positive velocity at inlet and positive velocity in continuum bu the direction of my cordinate system was with x axis directed in the same direction of boat advancing motion,so,to define velocity in continum i must use a negative value because water come forth my boat...differently i was experiencing vertices waves...the hell..
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Old   September 25, 2009, 06:17
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When I understand you right you didn't had seen/known that the velocity in the initial conditions is according the laboratory coordiante system?

Ok when I look at your picture know I see it.
X-axle shows to the left so you must work with negativ flow when the flow direction is from left to right
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Old   September 25, 2009, 06:22
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Quote:
Originally Posted by Maddin View Post
When I understand you right you didn't had seen/known that the velocity in the initial conditions is according the laboratory coordiante system?

Ok when I look at your picture know I see it.
X-axle shows to the left so you must work with negativ flow when the flow direction is from left to right
yes!but at inlet,flow direction is utomatically defined inlet to outlet..isn't it?
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Old   September 25, 2009, 06:43
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Under Physics Conditions of the Boundary you can set the flow direction
You can also give a vector for the flow or "normal to boundary" or a angle.
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Old   September 25, 2009, 06:47
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ok...the solution is:
be sure x axys si oriented as flow motion direction ...it is easyer...
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