CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CFX

not getting convergence

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 21, 2008, 10:41
Default not getting convergence
  #1
NVSD BABU
Guest
 
Posts: n/a
HI

iam working on simple natural convection problem. i have taken a copper plate of 1250*80*5mm and placed vertically in a steel enclosure of size 1630*510*150 and 2mm steel thickness.steel enclosure opened at bottom and closed at top.

for analysis i have considered only copper plate and air inside the steel encloser,i have given inflation mesh to air,which is having around 105000 elements.i have given copper-air interfaces. I have given opening boundary condition to bottom portion of air and all other outer faces declared as adiabatic walls.my model's vertical direction is y , i have given density as -9.81 in Y direction.tarbulence model used is k-e.I have tried both idealgas and air at 25 degC.i have tried different time steps for air and copper.

Plese help me

Thanks a lot

NVSD BABU

  Reply With Quote

Old   November 22, 2008, 07:19
Default Re: not getting convergence
  #2
NVSD BABU
Guest
 
Posts: n/a
hi plz find the geometry and give the comments that i have to follow

http://img153.imageshack.us/img153/4...mainlr5.th.png

  Reply With Quote

Old   November 24, 2008, 12:35
Default Re: not getting convergence
  #3
pratik mehta
Guest
 
Posts: n/a
Hi,

Could you please tell what kind of convergence issue are you facing, is your problem diverging or you simply not achieving the residual lower limit?.

thanks,,

  Reply With Quote

Old   November 25, 2008, 01:14
Default Re: not getting convergence
  #4
NVSD BABU
Guest
 
Posts: n/a
thank you pratik

i have given convergence as 1e-4, v-momentum not getting converged, it is oscillating and all other u,w and p getting 1e-4 convergence,but they are also oscillating.

Thank you NVSD BABU
  Reply With Quote

Old   November 25, 2008, 04:55
Default Re: not getting convergence
  #5
pratik mehta
Guest
 
Posts: n/a
Is it is high resolution scheme that you are running with or blend factor, kindly switch on the double precision tab as well, what is your global Y plus range and let me know more about the moniter points if at all you have

best of luck
  Reply With Quote

Old   November 25, 2008, 08:08
Default Re: not getting convergence
  #6
NVSD BABU
Guest
 
Posts: n/a
Thanks pratik, i will try with double precision.

I have tried high resolution,upwind and blend factor1 schemes.

Maximum mesh expansion factor is 70.1

moniter point is temperature.

Thanks

  Reply With Quote

Old   November 25, 2008, 08:22
Default Re: not getting convergence
  #7
NVSD BABU
Guest
 
Posts: n/a
hi prathik

global Y+ range is 0 to 3.412

Thanks
  Reply With Quote

Old   November 25, 2008, 16:59
Default Re: not getting convergence
  #8
Pratik Mehta
Guest
 
Posts: n/a
Sounds all basic settings seems good, are you solving it steady state or unsteady state . Try running with smaller time steps . First use K epsilon model and first order trasient case. Let me know what happens then
  Reply With Quote

Old   November 26, 2008, 05:04
Default Re: not getting convergence
  #9
NVSD BABU
Guest
 
Posts: n/a
thanks prathik

I am solving the problem as steady state.If i do in trasient state,please tell me how to take total duration and time steps. practically, to get convergence our model took 4hrs. do i give 4hrs as total duration.

Thanks

  Reply With Quote

Old   November 26, 2008, 22:49
Default Re: not getting convergence
  #10
Glenn Horrocks
Guest
 
Posts: n/a
http://www.cfd-online.com/Wiki/Ansys...gence_criteria
  Reply With Quote

Old   November 27, 2008, 09:36
Default Re: not getting convergence
  #11
pratik mehta
Guest
 
Posts: n/a
You need to find out the suitable timescale of your problem in way from the velocity lenght scale and the integral lenght scale , but usually it is so straight forward for complex geometries , in that case you can iterate your time scale factor starting from the time scale factor that CFX uses during the steady state calculation , we can get this number from the output file.

So run trasient with Kepsilon n first order ... i hope your fluid properties are reasonably quoted , anyways try out this and lets see what you get
  Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Convergence Centurion2011 FLUENT 24 May 9, 2015 08:02
problem with Min/max rho tH3f0rC3 OpenFOAM 7 February 23, 2013 06:37
Force can not converge colopolo CFX 13 October 4, 2011 22:03
Convergence of CFX field in FSI analysis nasdak CFX 2 June 29, 2009 01:17
Defect correction and convergence ganesh Main CFD Forum 4 June 30, 2006 14:20


All times are GMT -4. The time now is 09:52.