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

porous media convergence help

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 7, 2004, 16:27
Default porous media convergence help
  #1
Brian
Guest
 
Posts: n/a
I'm simulating unidirectional flow through a porous media (a tube bank). I've estimated the intertial resistance coefficient in the direction of flow through the porous region to be on the order of 3.5e+06, and to constrain the flow to the direction of the tubes, i've set the inertial resistance in the other two directions to be 3.5e+08.

The flow seems to be acting the way i would expect it to, but I am having trouble getting my solution to converge. Does anyone have any suggestions on what i can do to help my solution converge?
  Reply With Quote

Old   September 7, 2004, 18:53
Default Re: porous media convergence help
  #2
AJ
Guest
 
Posts: n/a
Start with laminar flow and then turn on turbulence if any...
  Reply With Quote

Old   September 8, 2004, 03:47
Default Re: porous media convergence help
  #3
gelisli
Guest
 
Posts: n/a
Hi Brian,

the coefficients seem to be viscous resistances not inertial. Could you please explain me how you calculate it?
  Reply With Quote

Old   September 8, 2004, 08:17
Default Re: porous media convergence help
  #4
Brian
Guest
 
Posts: n/a
Gelisli, Thanks for the response. I thought the same thing about the resistance being more viscous rather than inertial. However, when using the viscous resistance, i was unable to restrict the flow to a single direction to simulate flow through a tube bank. These simulations yielded large swirling flows within the 'porous' tube bank... a kind soul on this forum pointed out a brief mention in the fluent help file on simulating tube banks and it suggests to neglect the viscous resistance factors and use only inertial. Seems strange, but it works to constrain unidirectional flow. As for estimating the coefficients: the fluent help file porous media section has some equations for estimating the viscous and inertial resistance coefficients for beds of packed particles. these equations are funcions of the particled diameter, and the void fraction of pourous region. I equated the surface area of the opening of one of my 'tube bank' tubes to the surface area of the gap between three theoretical particles. I used the diameter of these theoretical particles in the coefficient equations along with the actual calculated void fraction of my tube bank {oops, i just realized that i grossly underestimated the void fraction previously which now lower my inertial coefficient by several orders of magnitude, perhaps my convergence problem will go away now}

well i guess trying to explain your problem to someone else is the best medicine sometimes...

while i'm posing: does anyone know of a good way to estimate the inertial viscous resistance coefficients for a tube bank (other than experimentally)?
  Reply With Quote

Old   September 8, 2004, 14:52
Default Re: porous media convergence help
  #5
Bak_Flow
Guest
 
Posts: n/a
Hi Brian,

The resistance coeficients for various geometries of grid banks, tube banks, and structures (of which a packed bed which you had used is one of the simplest) have been measured and correlated in several places. Probably the most extensive that I have seen is:

Flow Resistance: A Design Guide for Engineers I.E. Idelchik, July 1989

There also are some tabulations in various heat exchanger design handbooks and textbooks. One that I remember being particularly useful is in:

Adrian Bejan's "Convection Heat Transfer". There you will see an nice little explanation of the viscous and inertial resistance coeficients and how the relative importance changes with Reynolds number. This goes toward answering your question regarding the importance of the 2.

In my experience for most devices with tube banks and "normal fluids" ie air, water, steam, light hydrocarbons, etc the dominant effect is the inertial term. This would of course change for nano-scale devices or heavy oils, etc.

Best Regards,

Bak_Flow
  Reply With Quote

Old   September 9, 2004, 03:46
Default Re: porous media convergence help
  #6
gelisli
Guest
 
Posts: n/a
Hi Brian,

I have done several porous media calculations (not tube banks) using viscous resistance coefficients and it really works well. Actually I always use 1000 times larger coefficients for non flow directions and convergence never be a problem.

Regards,

  Reply With Quote

Old   February 22, 2012, 06:44
Default Divergence
  #7
New Member
 
Conor Doolan
Join Date: Oct 2011
Posts: 2
Rep Power: 0
Conor_1990 is on a distinguished road
Hi,

I'm trying to set up a fairly basic 2D model of flow through a tube bank which I have modelled as a porous media. However as soon as fluent carries out 1 iteration the solution diverges rapidly. Could this be a problem with boundary conditions.

I am using ANSYS 14.0 with fluent as my solver. I have set the porous zone as a "porous jump" is this the correct way to approach the problem?
Conor_1990 is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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
Multiphase Porous Media Flow - Convergence Issues VT_Bromley FLUENT 7 May 14, 2020 17:34
Porous media setup issues in Fluent Bernard Van FLUENT 29 January 26, 2017 05:09
Force can not converge colopolo CFX 13 October 4, 2011 23:03
Porous media and convergence A.Joshi FLUENT 0 October 21, 2003 23:09
porous media: Fluent or Star-CD? Igor Main CFD Forum 0 December 5, 2002 16:16


All times are GMT -4. The time now is 08:17.