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

steady state reached

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 9, 2006, 11:48
Default steady state reached
  #1
rajni
Guest
 
Posts: n/a
I am running a transient simulation ( transient due to a heat source inside a room). How to decide that a steady state has been attained after seemingly sufficient number of iterations ? What's the significance of "convergence" in such a situation ? I hope it doesn't indicate steady state.

Thanx in advance. -Rajni
  Reply With Quote

Old   June 10, 2006, 01:06
Default Re: steady state reached
  #2
Swarup
Guest
 
Posts: n/a
Steady state denotes "uniformity in time" at a position (of your choice) while spacial homogeneity may or may not exist.

Convergence is an indication of numerical accuracy of solution. You need numerical accuracy per time step for truly "time accurate" solution.

Some times, you just need a snapshot in time say a duartion of 1 hour (physical) and may not be concrened about steady state. I am not sure but natural convection is such a situation.

Swarup.
  Reply With Quote

Old   June 10, 2006, 13:12
Default Re: steady state reached
  #3
rajni
Guest
 
Posts: n/a
Thanx Swarup. But how can I check in my case that steady state conditions have reached ? I have a room with two windows in which a heat source is kept. Cold air enters the room from one window and leaves from the other. I can obtain profiles alright. But is there no other means of ascertaining that ?

Regards, rajni
  Reply With Quote

Old   June 10, 2006, 23:52
Default Re: steady state reached
  #4
Swarup
Guest
 
Posts: n/a
Try to track air temperature with time at out window. If you have reached a steady state, it should settle to a nominally constant vale. Use monitor panel to track this temperature/its average value. Steady state is a physically realizable case to some extent. Hence, it is most appropriate that you look at variable/s which attain a time invariant value. If you are not interested in time acccrate values, then you may afford to have somewhat large time steps (within the stability limit); so called false transient approach. The solution may converge numerically and then may reach a steady state value eventually. I guess natural convection is inherently transient phenomenon.

Swarup.

  Reply With Quote

Old   June 11, 2006, 05:11
Default Re: steady state reached
  #5
rajni
Guest
 
Posts: n/a
Thanx swarup for your reply ! I won't try your suggestion but I like the way you send detailed replies. What do you do, by the way ? Regards, Rajni
  Reply With Quote

Old   June 20, 2006, 04:03
Default Re: steady state reached
  #6
Rajeev Kumar Singh
Guest
 
Posts: n/a
In any unsteady state calculation the best way to find whether steady state has been reached is by monitoring certian parameters at the point of interest. In your case certainly the temperature fits the bill as Swarup pointed out. Convergence criteria only looks after accuracy of the solution within each time step. So convergence only cannot be the true indicator. So it is better to use monitors also even when you are solving in steady state. Good convergence does not mean correct solution.
  Reply With Quote

Old   June 28, 2006, 15:15
Default Re: steady state reached
  #7
Amr
Guest
 
Posts: n/a
Hi Rajini,

Are you working on fire/smoke simulation inside rooms?

Thanks,

Amr

  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
Solver for transonic flow? Martin Hegedus OpenFOAM Running, Solving & CFD 21 April 27, 2015 11:02
Constant velocity of the material Sas CFX 15 July 13, 2010 08:56
mass flow in is not equal to mass flow out saii CFX 2 September 18, 2009 08:07
Monitor point values in a steady state simulation Kushagra CFX 2 July 13, 2008 20:03
plz help,urgent, vof model steady state Garima Chaudhary FLUENT 2 May 30, 2007 04:38


All times are GMT -4. The time now is 17:09.