periodic boundary condition

rasool motamedi · May 14, 2013, 16:07

hi

I am simulating a channel with mixer in 2D.
the velocity profile of inlet and outlet in channel must be similar and equal
but their pressure are not similar
it is like periodic boundary condition with mass flow rate defined but i don't want that mass flow from outlet come to inlet because they are mixed and my inlet must be unmixed
how can create this condition?
in past i tried to make it with periodic interface constant mass flow rate but my outlet mixed component goes to inlet
now I actived gravity along the channel and I am wating for answer.
thanks regard

ghorrocks · May 14, 2013, 21:14

Can you explain it a bit better? Why must the inlet and outlet be similar and equal? Do you have multiple of these things lined up?

If the mixture builds up in each row you need to put something in the periodic boundary to handle that. Because your flow is not actually periodic - the mixture builds up each row - so you have to make some of it disappear so it can be periodic.

rasool motamedi · May 15, 2013, 08:43

hi
thank for your attentions
this is my channel
Fluid Flow CFX_001.jpg

and my inlet velocity profile is as follow:
Chart inlet.jpg

and my outlet velocity profile is as follow:
Chart.jpg

I want that in any time step my inlet velocity profile be like outlet

but mixed fluids don't enter to inlet.

in periodic condition mixed fluids enter too.

ghorrocks · May 15, 2013, 09:46

If you use a periodic pair to join the inlet and outlet then the flow will just evolve to whatever profile the periodic flow generates. You don't impose it, it is an output of the simulation. And the inlet will match the outlet, that is how periodic boundaries work.

And you will not be able to model the mixing you show here as it is not even close to periodic. But it looks close to fully mixed even after one mixer so it is just going to stay mixed all the way through. Or do you need to be more precise about the level of mixing? If so, why?

rasool motamedi · May 15, 2013, 11:00

hi
I am validating my friend's project that has done with SPH and his conditions are this like.
and some other papers have done this work with boltzman method.
I am sure that CFX can do it with a CEL or other things.
Now I am searchig in mesh conection
thanks

rasool motamedi · May 17, 2013, 17:00

hi
Always I have application error in cfd post and i can not see all of my transient results and only I see final result.

Do you know why?
thaanks regards

how can save all of transient results?
where can save variables?
Only I can see final result?

ghorrocks · May 17, 2013, 20:14

There is another question on the forum at the moment on the results file thing. That thread does not have a solution (yet) but have a look at it for the discussion.

May 14, 2013, 16:07	periodic boundary condition	#1
rasool motamedi Member rasool Join Date: Apr 2013 Posts: 41 Rep Power: 13	hi I am simulating a channel with mixer in 2D. the velocity profile of inlet and outlet in channel must be similar and equal but their pressure are not similar it is like periodic boundary condition with mass flow rate defined but i don't want that mass flow from outlet come to inlet because they are mixed and my inlet must be unmixed how can create this condition? in past i tried to make it with periodic interface constant mass flow rate but my outlet mixed component goes to inlet now I actived gravity along the channel and I am wating for answer. thanks regard

May 15, 2013, 09:46		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	If you use a periodic pair to join the inlet and outlet then the flow will just evolve to whatever profile the periodic flow generates. You don't impose it, it is an output of the simulation. And the inlet will match the outlet, that is how periodic boundaries work. And you will not be able to model the mixing you show here as it is not even close to periodic. But it looks close to fully mixed even after one mixer so it is just going to stay mixed all the way through. Or do you need to be more precise about the level of mixing? If so, why? rasool motamedi likes this.

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May 14, 2013, 21:14		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Can you explain it a bit better? Why must the inlet and outlet be similar and equal? Do you have multiple of these things lined up? If the mixture builds up in each row you need to put something in the periodic boundary to handle that. Because your flow is not actually periodic - the mixture builds up each row - so you have to make some of it disappear so it can be periodic.

May 15, 2013, 08:43		#3
rasool motamedi Member rasool Join Date: Apr 2013 Posts: 41 Rep Power: 13	hi thank for your attentions this is my channel Fluid Flow CFX_001.jpg and my inlet velocity profile is as follow: Chart inlet.jpg and my outlet velocity profile is as follow: Chart.jpg I want that in any time step my inlet velocity profile be like outlet but mixed fluids don't enter to inlet. in periodic condition mixed fluids enter too.

May 15, 2013, 11:00		#5
rasool motamedi Member rasool Join Date: Apr 2013 Posts: 41 Rep Power: 13	hi I am validating my friend's project that has done with SPH and his conditions are this like. and some other papers have done this work with boltzman method. I am sure that CFX can do it with a CEL or other things. Now I am searchig in mesh conection thanks

May 17, 2013, 17:00		#6
rasool motamedi Member rasool Join Date: Apr 2013 Posts: 41 Rep Power: 13	hi Always I have application error in cfd post and i can not see all of my transient results and only I see final result. Do you know why? thaanks regards how can save all of transient results? where can save variables? Only I can see final result?

May 17, 2013, 20:14		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	There is another question on the forum at the moment on the results file thing. That thread does not have a solution (yet) but have a look at it for the discussion.