pipe

hamid1 · June 29, 2011, 04:16

Hi Guys

in pipe with pressure boundary condition is it needed to have long domain? or any arbitrary length of pipe is fine for numerical calculation,

shimmyya · June 29, 2011, 07:17

as far as i know u dont need any specific length for solve ur problem, but if u want to see the full developed flow u need a certain length

hamid1 · June 29, 2011, 08:55

In modeling fluid flow in a pipe, when do I need to see the fully developed flow? (either of laminar or turbulent regime)
Do I need specific length in inlet or outlet?
What is the criterion for that?
I was thinking that if after any modeling there wouldn’t be any circulation (which cause back flow) in openings the length is enough (either of inlet or outlet), is it true?

shimmyya · June 29, 2011, 09:53

hi,
1. it depends on you if u want to see any full developed flow. For example u have something in ur pipe and want to see how ur fluid pass it and how turbulent it will be.
2. still as far as i know in fluent u dont need any specific length, the solver will give u same results so if u solve ur modell with 10m length and anothertime with 1m length, this first meter should allways have same values.
3. ur last sentence i dont get

hamid1 · June 29, 2011, 10:07

Thank u very much for reply, I think the main issue is if flow passing through opposite direction in openings or not, say, in inlet flow coming from inside the domain to outside and in case of outlet if flow coming from outside of the domain to inside … if it dosent happen then the simulation is correct from this point of view (regardless of whatever the length of the pipe is), u may correct me please if I am wrong,
Thanks in advance
Hamid

shimmyya · June 29, 2011, 10:45

hi,
thats right, the flow dont come back from outside. but i guess if u have backflow in ur pipe, its possible that flow left pipe through inlet.
Because i dont know it 100%,i guess i will try to simulate it in next time

edit: hmm seems i was on wrong way ... if u look at image u see that there is a little bit diffrence

hamid1 · June 29, 2011, 12:16

So.. u mean at same cross section there are different results for longer and shorter length of the pipe, ... if so how long do u use for a domain to get rid of this issue?

and what if u have only the boundary condition of short length ? (though this is not my case but just asking)

June 29, 2011, 04:16	pipe	#1
hamid1 Senior Member hamid Join Date: Nov 2010 Posts: 185 Rep Power: 15	Hi Guys in pipe with pressure boundary condition is it needed to have long domain? or any arbitrary length of pipe is fine for numerical calculation,

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June 29, 2011, 07:17		#2
shimmyya New Member eddy Join Date: Apr 2011 Posts: 8 Rep Power: 15	as far as i know u dont need any specific length for solve ur problem, but if u want to see the full developed flow u need a certain length

June 29, 2011, 08:55		#3
hamid1 Senior Member hamid Join Date: Nov 2010 Posts: 185 Rep Power: 15	In modeling fluid flow in a pipe, when do I need to see the fully developed flow? (either of laminar or turbulent regime) Do I need specific length in inlet or outlet? What is the criterion for that? I was thinking that if after any modeling there wouldn’t be any circulation (which cause back flow) in openings the length is enough (either of inlet or outlet), is it true?

June 29, 2011, 09:53		#4
shimmyya New Member eddy Join Date: Apr 2011 Posts: 8 Rep Power: 15	hi, 1. it depends on you if u want to see any full developed flow. For example u have something in ur pipe and want to see how ur fluid pass it and how turbulent it will be. 2. still as far as i know in fluent u dont need any specific length, the solver will give u same results so if u solve ur modell with 10m length and anothertime with 1m length, this first meter should allways have same values. 3. ur last sentence i dont get

June 29, 2011, 10:07		#5
hamid1 Senior Member hamid Join Date: Nov 2010 Posts: 185 Rep Power: 15	Thank u very much for reply, I think the main issue is if flow passing through opposite direction in openings or not, say, in inlet flow coming from inside the domain to outside and in case of outlet if flow coming from outside of the domain to inside … if it dosent happen then the simulation is correct from this point of view (regardless of whatever the length of the pipe is), u may correct me please if I am wrong, Thanks in advance Hamid

June 29, 2011, 12:16		#7
hamid1 Senior Member hamid Join Date: Nov 2010 Posts: 185 Rep Power: 15	So.. u mean at same cross section there are different results for longer and shorter length of the pipe, ... if so how long do u use for a domain to get rid of this issue? and what if u have only the boundary condition of short length ? (though this is not my case but just asking)