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Old   June 28, 2013, 03:51
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hello everyone,

my cas is a 'T' tube connected by two cylindres with an inlet and 2 outlet.
the fluide is turbulent. i made the boundary condition as 'outflow', the warning came to me was "reversed flow". i looked for the former thread, it is said that i could change it to 'pressure outlet'. after operation, the warning is always "reversed flow".
does someone know what happened?

thank you
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Old   June 28, 2013, 06:33
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you have a vortex crossing the outlet.
It is just a warning, let iterate, the warning may disappear
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Old   June 28, 2013, 06:36
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Extend your computational domain at the outlets, i.e. ensure that the outlet is far away from the tee
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Old   June 28, 2013, 07:46
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Ok, thank you, i will wait a bit.
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Old   June 28, 2013, 07:48
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Quote:
Originally Posted by azt View Post
Extend your computational domain at the outlets, i.e. ensure that the outlet is far away from the tee
Thank you. in this case the distance of outlets are at least 25 times that of diameter
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Old   June 28, 2013, 07:54
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Quote:
Originally Posted by -mAx- View Post
you have a vortex crossing the outlet.
It is just a warning, let iterate, the warning may disappear
hello, Maxime,this is what i get. do you have some suggestions?
https://www.dropbox.com/s/30deqc29eq...ed%20flow.docx
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Old   June 28, 2013, 08:44
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Originally Posted by steven1 View Post
hello, Maxime,this is what i get. do you have some suggestions?
https://www.dropbox.com/s/30deqc29eq...ed%20flow.docx
you have a convergence problem, and I don't think it comes to your reversed flow
-check Mesh
-how are your turbulent bc?
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Old   June 28, 2013, 08:58
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Quote:
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you have a convergence problem, and I don't think it comes to your reversed flow
-check Mesh
-how are your turbulent bc?
the mesh is not too bad. i chose the standard wall function. here are the informations https://www.dropbox.com/s/30deqc29eq...ed%20flow.docx
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Old   June 28, 2013, 09:19
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-what is the quality of worst element? (show worst element option in gambit)
-what are the tubulent bc at your inlet (you showed the turbulent model)
-did you scaled your model?
-can you copy and paste the output from checkMesh
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Old   June 28, 2013, 09:46
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Quote:
Originally Posted by -mAx- View Post
-what is the quality of worst element? (show worst element option in gambit)
-what are the tubulent bc at your inlet (you showed the turbulent model)
-did you scaled your model?
-can you copy and paste the output from checkMesh
hello, this is the information. thank you
https://www.dropbox.com/s/xml8ctvagskchbf/0628-2.docx


Mesh Quality:
Orthogonal Quality ranges from 0 to 1, where values close to 0 correspond to low quality.
Minimum Orthogonal Quality = 2.75142e-01
Maximum Aspect Ratio = 1.61014e+01
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Old   June 28, 2013, 09:50
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ok, your mesh is ok and seems to be scaled
in the velocity BC, you should have turbulent parameters, waht do you have?
How is you material? density, viscosity?
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Old   June 28, 2013, 10:01
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ok, your mesh is ok and seems to be scaled
in the velocity BC, you should have turbulent parameters, waht do you have?
How is you material? density, viscosity?
i have the parameters of K and epsilon. k=0.053985 and epsilon=1.4722. the velocity is 5m/s, it is calculated with the Re=100000. the material is water-liquid. density is about 1000kg/m3, and viscosity is about 0.001kg/m-s
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Old   June 28, 2013, 10:15
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Ok I have to hurry
Try to switch with realizable-kepsilon
Try with and without enhanced wall treatment
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Old   June 28, 2013, 10:21
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sorry, i didn't understand what you mean 'realizable-kepsilon'. the k,epsilon values that i used are also calculated with Re=100000.
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Old   June 28, 2013, 10:43
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Originally Posted by steven1 View Post
sorry, i didn't understand what you mean 'realizable-kepsilon'. the k,epsilon values that i used are also calculated with Re=100000.
Other turbulence model
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Old   July 2, 2013, 03:33
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Quote:
Originally Posted by -mAx- View Post
Other turbulence model
hello Max, i have tried the realizable k-epsilon, but the situation didn't change, there are still problem of conbergence and warnings of reversed flow. By the way, the Y+ is between 5 and 30.
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Old   July 2, 2013, 05:12
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Hi,

I have same problem and I think it is the boundary conditions imposed on your two outputs which poses the problem .. when you have two output can not impose "pressure" at outlet..

What are your boundary conditions at the outlets??



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Originally Posted by steven1 View Post
hello Max, i have tried the realizable k-epsilon, but the situation didn't change, there are still problem of conbergence and warnings of reversed flow. By the way, the Y+ is between 5 and 30.
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Old   July 2, 2013, 05:24
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Hi,

I have same problem and I think it is the boundary conditions imposed on your two outputs which poses the problem .. when you have two output can not impose "pressure" at outlet..

What are your boundary conditions at the outlets??
I use outflow as the BC of outlet. in fact, i had wanted to try the pressure outlet, but i don't know the factors that i have to fill
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Old   July 2, 2013, 08:20
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The condition of pressure outlet is valid when we have "one outlet" for two and more of outlet this condition is not valid, you must use the "equal flow rate" at outlets.. try to reduce the underelaxation at the minimum (0.1 or 0.2)


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I use outflow as the BC of outlet. in fact, i had wanted to try the pressure outlet, but i don't know the factors that i have to fill
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Old   July 2, 2013, 08:23
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Quote:
Originally Posted by rayan24 View Post
The condition of pressure outlet is valid when we have "one outlet" for two and more of outlet this condition is not valid, you must use the "equal flow rate" at outlets.. try to reduce the underelaxation at the minimum (0.1 or 0.2)
so what should I put as the gauge pressure?
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