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

Urgent help: RMS problem!!!

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

Reply
 
LinkBack Thread Tools Display Modes
Old   September 4, 2007, 18:40
Default Urgent help: RMS problem!!!
  #1
Anh
Guest
 
Posts: n/a
Hi all,

I am modeling heat transfer between solid and liquid with phase change. The geometry is quite simple. They are two cubic and i meshed it by CFX. When i run it in transisent, even though i set the time step very small (2e-10 second, total time for my simulation=1e-6 second), RMS is strongly fluctuation. RMS is below 1e-4 but it's up and down which create a row of color. Domain imbalance is very good (below 0.1%).

So, if the RMS is fluctuation but domain imbalance is good, the result is applicaple? Anybody know how to fix it??? Pls. advise me.

Thank in advance.
  Reply With Quote

Old   September 6, 2007, 10:46
Default Re: Urgent help: RMS problem!!!
  #2
Omer
Guest
 
Posts: n/a
Well, for most of the transient analysis, it is only normal that the RMS would fluctuate for each substep in the iteration!

How good is your solution can only be verified by comparing it with a real case.

And you need to be really sure if 1e-4 does really give you a convergent result. If you have a monitor point of some kind when you run the steady state solution, you would get to know when a good amount of convergence is reached.
  Reply With Quote

Old   September 7, 2007, 22:44
Default Re: Urgent help: RMS problem!!!
  #3
TB
Guest
 
Posts: n/a
What RMS are you using? It could be due to the way you set up the problem too.
  Reply With Quote

Old   September 8, 2007, 02:28
Default Re: Urgent help: RMS problem!!!
  #4
Anh
Guest
 
Posts: n/a
Thank you Omer and TB.

I set RMS=1e-4. My model is quite sensitive with mesh and tiem step. I tried to reduce mesh size and time step but it still oscillation.

Anybody know how to mesh by hex element? My current mesh is tet and prism then i think it's not good enough.

Thanks in advanced
  Reply With Quote

Old   September 8, 2007, 13:47
Default Re: Urgent help: RMS problem!!!
  #5
Omer
Guest
 
Posts: n/a
If you are using CFX Mesh , you wouldn't get a Hex mesh.

Depends on what kinda meshing tool you would be putting to use.
  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
Urgent problem - orthotropic material in ICEM Luk CFX 6 August 30, 2006 08:06
Urgent plotting problem in Post...Please help. Alan CFX 1 March 28, 2005 18:46
Multiphase Problem (Urgent) Dadang CFX 4 June 21, 2004 07:46
Urgent help on Sand casting problem arunprasad FLUENT 0 April 18, 2004 05:04
An urgent problem, HELP!!! Fanadam FLUENT 1 May 2, 2003 23:38


All times are GMT -4. The time now is 01:12.