CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

Density boussinesq Problem

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 27, 2007, 08:31
Default Density boussinesq Problem
  #1
matrix-1.0
Guest
 
Posts: n/a
Hi, I am simulation a big entry hall and try to activate the variable density option.

Under Material Air I activate "boussinesq" and set the default Density to 1.19 Kg/m³ and the thermal expansion coeff. 1/k to 0.003 ( 1:300K ). the other values are not changed.

Then, under Operation Conditions, I leave the 15 °C under boussinesq and mark the variable density parameter and set the density there to 1.225.

The iteration becomes convergent, even unsteady, but under display/contors/density it ranges between 1.18999 and 1.190001

So is my setting wrong, or is there a different view panel ?

My temperatures in this hall range fom 14 °C to 80 °c so there should be more...

Can anybody help me out, please ???

  Reply With Quote

Old   July 27, 2007, 12:01
Default Re: Density boussinesq Problem
  #2
Ken Adams
Guest
 
Posts: n/a
Hello,

Just one quick thought. Boussinesq approximation is only valid for small temperature variations (Fluent manual 12.5.3). So according to your temperature range, that approximation may not work. There're several posts on natural convection problems on this forum. Lots of people suggest using "Ideal Gas" for density.

Hope it helps,

Ken
  Reply With Quote

Old   July 29, 2007, 18:33
Default Re: Density boussinesq Problem
  #3
matrix-1.0
Guest
 
Posts: n/a
Hi, thanks for your advice ! It really helped. The density now behaves as it should ! But..., now I do not get it convergent. The continuity is constant at 1e-01 and the other parameters at 1e-02. I am using a Do radiation with solar calculator. Can this be the problem in conjunction with a non constant density ? ( with constant density it becomes convergent after 800 Iterations ) I tried changing the under-rellaxation factors pressure and momentunm, sadly to no avail. Then I changed the density rell. to 0.3, that also didn't help.

Does any body has an idea ??

  Reply With Quote

Old   July 30, 2007, 05:08
Default Re: Density boussinesq Problem
  #4
ritmat
Guest
 
Posts: n/a
the problem could be if you are using gravity. If it is the case in operating conditions decrease the gravity , and increase step by step waiting for convergence. Sometimes it can be the problem. let us know
  Reply With Quote

Old   July 30, 2007, 11:14
Default Re: Density boussinesq Problem
  #5
matrix-1.0
Guest
 
Posts: n/a
Hi, thanks for this advice, but I am not allowed to reduce the gravity. Could you please tell me where I can increase the sep by step waiting ??

Many thanks !
  Reply With Quote

Old   July 31, 2007, 03:02
Default Re: Density boussinesq Problem
  #6
ritmat
Guest
 
Posts: n/a
i mean run your model with 0.001 m/s2 ( or less) and wait convergence. Then increase little by little and do the same until 9.81.

  Reply With Quote

Old   August 1, 2007, 08:05
Default Re: Density boussinesq Problem
  #7
matrix-1.0
Guest
 
Posts: n/a
Ah, understood !!

I will do it and let you now !

Many thanks !!! Matrix
  Reply With Quote

Old   August 4, 2007, 08:08
Default Re: Density boussinesq Problem
  #8
matrix-1.0
Guest
 
Posts: n/a
Hi, thanks al lot ! It really worked !!! I started wit 0.001 went to 1 then to 5 and at last to 9.81.

Many thanks !!! Matrix
  Reply With Quote

Old   January 17, 2014, 22:05
Default
  #9
Senior Member
 
Join Date: Jan 2012
Posts: 197
Rep Power: 14
itsme_kit is on a distinguished road
Quote:
Originally Posted by matrix-1.0
;144146
Hi, thanks al lot ! It really worked !!! I started wit 0.001 went to 1 then to 5 and at last to 9.81.

Many thanks !!! Matrix
Hi

I wonder why we need to try different value of gravity acceleration

If we do so, I have to run several times, what's the point of doing this

Shouldn't the gravity acceleration be a constant value in 9.81

Thanks for your reply
itsme_kit is offline   Reply With Quote

Old   January 17, 2014, 22:17
Default
  #10
Senior Member
 
Join Date: Jan 2012
Posts: 197
Rep Power: 14
itsme_kit is on a distinguished road
Quote:
Originally Posted by ritmat
;144006
i mean run your model with 0.001 m/s2 ( or less) and wait convergence. Then increase little by little and do the same until 9.81.
Hi I wonder why we need to change the value of gravity acceleration

Shouldn't it be a constant value in 9.81

Thanks in advance for your help
itsme_kit is offline   Reply With Quote

Reply


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Problem with rhoSimpleFoam : exploding enthalpy and density at the walls david39 OpenFOAM Running, Solving & CFD 6 January 18, 2011 12:49
Velocity profiles problem behind the elbow (3D problem) kabat73 FLUENT 8 May 9, 2010 05:26
Density problem ato FLUENT 0 March 11, 2008 08:17
Problem on high density ratio in Level Set method Kai Yan Main CFD Forum 10 December 25, 2007 07:12
Roe-averaged Density Nishikawa Main CFD Forum 19 April 4, 2000 00:08


All times are GMT -4. The time now is 05:21.