Natural Convection BC

yipseng · January 19, 2010, 09:25

I'm doing my final year project on Natural Convection in fin array.. I investigate the Natural Convection of the air domain. I created 3D volume of air which partial of the face of that air volume is fin wall and base which temp constant, i set th BC as below:

Fin wall -Wall (constant temp 400K)
Fin base -Wall (constant temp 400K)
Other surface = Pressure inlet and outlet randomly (both oso "0" presure)

And

Operation Condition = 101325 pascal, 300K temp and tick gravity(y= -9.81)
Material = air with ideal gas
Solution Initialization = all zero value

Picture uploaded:
http://img210.imageshack.us/img210/357/fin2b.jpg
http://img402.imageshack.us/img402/5941/finmeshed.jpg

But i got error ms as:
----------------------------------------------------------------------
reversed flow in 650 faces on pressure-outlet 3.

reversed flow in 1248 faces on pressure-inlet 4.

reversed flow in 5000 faces on pressure-outlet 5.
10 2.6736e-01 2.8976e-05 5.2343e-02 2.4865e-02 3.7876e-08 0:00:00 0

No error handler available

Error: FLUENT received a fatal signal (SEGMENTATION VIOLATION).
Error Object: ()

Error message from graphics function Close_Segment:
Nothing open - can't Close a 'segment'

-------------------------------------------------------------------

Anyone tell me wat to do? I set the error bc?
thanks... I 'm a beginer here, hope ur help...

yipseng · January 23, 2010, 03:28

No one reply me?

rahulsharma · January 25, 2010, 01:07

Quote:

Originally Posted by yipseng

I'm doing my final year project on Natural Convection in fin array.. I investigate the Natural Convection of the air domain. I created 3D volume of air which partial of the face of that air volume is fin wall and base which temp constant, i set th BC as below:

Fin wall -Wall (constant temp 400K)
Fin base -Wall (constant temp 400K)
Other surface = Pressure inlet and outlet randomly (both oso "0" presure)

And

Operation Condition = 101325 pascal, 300K temp and tick gravity
Material = air with ideal gas
Solution Initialization = all zero value

But i got error ms as:
----------------------------------------------------------------------
reversed flow in 650 faces on pressure-outlet 3.

reversed flow in 1248 faces on pressure-inlet 4.

reversed flow in 5000 faces on pressure-outlet 5.
10 2.6736e-01 2.8976e-05 5.2343e-02 2.4865e-02 3.7876e-08 0:00:00 0

No error handler available

Error: FLUENT received a fatal signal (SEGMENTATION VIOLATION).
Error Object: ()

Error message from graphics function Close_Segment:
Nothing open - can't Close a 'segment'

-------------------------------------------------------------------

Anyone tell me wat to do? I set the error bc?
thanks... I 'm a beginer here, hope ur help...

hey this is rahul .........
i think you should use boussinesq model instead of ideal gas in the material selection panel of for air and set the appropriate thermal expansion coefficient....

yipseng · January 27, 2010, 04:19

Thanks rahul.. But izit ideal gas more suitable to which has large temp diff?
thermal expansion coefficient what value i should set? I jus set default value..

udayrg · January 27, 2010, 07:43

Hi, yipseng

Let us see how are the fins oriented , Are they horizontal of vertical W.R.T. gravity.

Once this is clear. You can find out whether the natural convection flow is laminar or turbulent.

In many cases where the flow is turbulent in natural convection cases it is tough to converge.

In that case you can reduce you gravity to 100 times run it in stage to reach the value of 9.81 m^2/sec.

Let me know the exact errors you encountered.

Uday

yipseng · January 27, 2010, 09:15

Picture uploaded.. Anyone noe what the problem??

Fiska · January 27, 2010, 11:08

I've got a problem with natural convection, too. The suggestion to check if flow is turbolent or laminar is surely good! In case of turbolent flow i suggest to use K-eps models.
Hi!

yipseng · February 2, 2010, 12:07

any 1 know how to solve? Thanks

denizen · February 3, 2010, 08:36

i know but it is you project, so you have to done it yourself.

best regards.

hook · February 4, 2010, 00:46

Dear Yapiseng, I happen to simulate the same model with you. But I set the fin base as heat flux and I consider the air-fin coupled domain. And I also set BC as symmetric and pressure-out. I did have solutions. I wonder if you have succeeded with a solution and what's the error. How much was that?
Maybe we could help each other.

January 19, 2010, 09:25	Natural Convection BC	#1
yipseng New Member YIP KOK SENG Join Date: Jan 2010 Posts: 6 Rep Power: 16	I'm doing my final year project on Natural Convection in fin array.. I investigate the Natural Convection of the air domain. I created 3D volume of air which partial of the face of that air volume is fin wall and base which temp constant, i set th BC as below: Fin wall -Wall (constant temp 400K) Fin base -Wall (constant temp 400K) Other surface = Pressure inlet and outlet randomly (both oso "0" presure) And Operation Condition = 101325 pascal, 300K temp and tick gravity(y= -9.81) Material = air with ideal gas Solution Initialization = all zero value Picture uploaded: http://img210.imageshack.us/img210/357/fin2b.jpg http://img402.imageshack.us/img402/5941/finmeshed.jpg But i got error ms as: ---------------------------------------------------------------------- reversed flow in 650 faces on pressure-outlet 3. reversed flow in 1248 faces on pressure-inlet 4. reversed flow in 5000 faces on pressure-outlet 5. 10 2.6736e-01 2.8976e-05 5.2343e-02 2.4865e-02 3.7876e-08 0:00:00 0 No error handler available Error: FLUENT received a fatal signal (SEGMENTATION VIOLATION). Error Object: () Error message from graphics function Close_Segment: Nothing open - can't Close a 'segment' ------------------------------------------------------------------- Anyone tell me wat to do? I set the error bc? thanks... I 'm a beginer here, hope ur help... Last edited by yipseng; January 27, 2010 at 09:13.

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January 23, 2010, 03:28		#2
yipseng New Member YIP KOK SENG Join Date: Jan 2010 Posts: 6 Rep Power: 16	No one reply me?

January 27, 2010, 04:19		#4
yipseng New Member YIP KOK SENG Join Date: Jan 2010 Posts: 6 Rep Power: 16	Thanks rahul.. But izit ideal gas more suitable to which has large temp diff? thermal expansion coefficient what value i should set? I jus set default value..

January 27, 2010, 07:43		#5
udayrg Member Join Date: Mar 2009 Posts: 32 Rep Power: 17	Hi, yipseng Let us see how are the fins oriented , Are they horizontal of vertical W.R.T. gravity. Once this is clear. You can find out whether the natural convection flow is laminar or turbulent. In many cases where the flow is turbulent in natural convection cases it is tough to converge. In that case you can reduce you gravity to 100 times run it in stage to reach the value of 9.81 m^2/sec. Let me know the exact errors you encountered. Uday

January 27, 2010, 09:15		#6
yipseng New Member YIP KOK SENG Join Date: Jan 2010 Posts: 6 Rep Power: 16	Picture uploaded.. Anyone noe what the problem??

January 27, 2010, 11:08		#7
Fiska New Member Daniele Join Date: Jan 2010 Posts: 8 Rep Power: 16	I've got a problem with natural convection, too. The suggestion to check if flow is turbolent or laminar is surely good! In case of turbolent flow i suggest to use K-eps models. Hi!

February 2, 2010, 12:07		#8
yipseng New Member YIP KOK SENG Join Date: Jan 2010 Posts: 6 Rep Power: 16	any 1 know how to solve? Thanks

February 3, 2010, 08:36		#9
denizen New Member Join Date: Mar 2009 Posts: 25 Rep Power: 0	i know but it is you project, so you have to done it yourself. best regards.

February 4, 2010, 00:46		#10
hook New Member Join Date: Jan 2010 Posts: 7 Rep Power: 16	Dear Yapiseng, I happen to simulate the same model with you. But I set the fin base as heat flux and I consider the air-fin coupled domain. And I also set BC as symmetric and pressure-out. I did have solutions. I wonder if you have succeeded with a solution and what's the error. How much was that? Maybe we could help each other.