Can I use turbulent model to solve a laminar flow?

nikhil · January 30, 2011, 23:16

Hello,

I am handling a transient case in which flow regime changes from laminar to turbulent in a non periodic fashion. There are shifts of laminar and turbluent regime in my case

If i select any turbulent model for this case, Will it produce correct results when the flow is in laminar regime?

Thanks,
Nikhil

swiftaircraft · January 31, 2011, 17:14

This will not produce the correct results. You need to set up a separate zones where you have laminar flow.

nikhil · January 31, 2011, 17:26

Well, Flow in the domain is transient. (Inlet velocity has period profile of multiple sines and cosins). Hence, sometimes entire flow is in laminar regime and sometimes (entirely) in turbulent regime.

Therefore, i am sure whether separation of zone would work in such case.
I am thinking about writing an UDF that will turn on/off the turbulence model depending upon the Re.

I just wanted to know, Is there any other better way to do that?

DoHander · January 31, 2011, 20:18

Use a transition model, in Fluent 12 and 13 you have two models that can handle transition from laminar to turbulent flow.

swiftaircraft · February 1, 2011, 04:33

nikhil I agree with DoHander. Also the use of a UDF to turn features on and off is in my experience bad as you lose many features of the flow. Namely in turning off turbulence based on Re you do not see the transition zone.

nikhil · February 1, 2011, 11:42

Thanks guys.
I will check the transition model.

January 30, 2011, 23:16	Can I use turbulent model to solve a laminar flow?	#1
nikhil New Member Nik Join Date: Mar 2010 Location: Michigan Posts: 25 Rep Power: 16	Hello, I am handling a transient case in which flow regime changes from laminar to turbulent in a non periodic fashion. There are shifts of laminar and turbluent regime in my case If i select any turbulent model for this case, Will it produce correct results when the flow is in laminar regime? Thanks, Nikhil

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January 31, 2011, 17:14		#2
swiftaircraft Member David Stanbridge Join Date: Apr 2010 Location: Norwich, UK Posts: 59 Rep Power: 16	This will not produce the correct results. You need to set up a separate zones where you have laminar flow.

January 31, 2011, 17:26		#3
nikhil New Member Nik Join Date: Mar 2010 Location: Michigan Posts: 25 Rep Power: 16	Well, Flow in the domain is transient. (Inlet velocity has period profile of multiple sines and cosins). Hence, sometimes entire flow is in laminar regime and sometimes (entirely) in turbulent regime. Therefore, i am sure whether separation of zone would work in such case. I am thinking about writing an UDF that will turn on/off the turbulence model depending upon the Re. I just wanted to know, Is there any other better way to do that?

January 31, 2011, 20:18		#4
DoHander Senior Member Join Date: Nov 2009 Posts: 411 Rep Power: 20	Use a transition model, in Fluent 12 and 13 you have two models that can handle transition from laminar to turbulent flow.

February 1, 2011, 04:33		#5
swiftaircraft Member David Stanbridge Join Date: Apr 2010 Location: Norwich, UK Posts: 59 Rep Power: 16	nikhil I agree with DoHander. Also the use of a UDF to turn features on and off is in my experience bad as you lose many features of the flow. Namely in turning off turbulence based on Re you do not see the transition zone.

February 1, 2011, 11:42		#6
nikhil New Member Nik Join Date: Mar 2010 Location: Michigan Posts: 25 Rep Power: 16	Thanks guys. I will check the transition model.