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

Difference results between Steady and Unsteady?

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

Like Tree1Likes
  • 1 Post By Bob (a Differrent bob)

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 30, 2004, 06:51
Default Difference results between Steady and Unsteady?
  #1
Giang T Vu
Guest
 
Posts: n/a
Hi all! I got different results when I change my model from steady to unsteady state (both states are converged successfully). What makes the unsteady results differ from the steady ones with the same conditions? thanks for help. Giang T Vu
  Reply With Quote

Old   April 30, 2004, 09:00
Default Re: Difference results between Steady and Unsteady
  #2
bob
Guest
 
Posts: n/a
I think in steady State in the Navier stokes equation they do not have transient terms. While in unsteady State case they have it. When you are problem is steady you will get convergence whether you use steady State or unsteady State solver. Pratap
  Reply With Quote

Old   April 30, 2004, 09:01
Default Re: Difference results between Steady and Unsteady
  #3
bob
Guest
 
Posts: n/a
I think in steady State in the Navier stokes equation they do not have transient terms. While in unsteady State case they have it. When you are problem is steady you will get convergence whether you use steady State or unsteady State solver. bob
  Reply With Quote

Old   May 1, 2004, 06:15
Default Re: Difference results between Steady and Unsteady
  #4
Giang T Vu
Guest
 
Posts: n/a
Thanks Bob, yes, mine is a steady state problem, when I change to run it under unsteady state it should give me the same result, correct? What would you say if I got the same pressure and velocity distribution and DIFFERENT vapor product (I'm modeling cavitation) when I switch from steady to unsteady mode?
  Reply With Quote

Old   May 4, 2004, 04:24
Default Re: Difference results between Steady and Unsteady
  #5
vladimir krejci
Guest
 
Posts: n/a
hi giang

what about your time step size and time dicretisation scheme?
  Reply With Quote

Old   May 6, 2004, 10:07
Default Re: Difference results between Steady and Unsteady
  #6
Giang T Vu
Guest
 
Posts: n/a
Hi Vladimir, The time step size deduced from Courant number and I estimated around 0.001. I used 1st order implicit segregated solver with standard k-epsilon turbulent model. Giang.
  Reply With Quote

Old   May 22, 2004, 07:37
Default Re: Difference results between Steady and Unsteady
  #7
Bob (a Differrent bob)
Guest
 
Posts: n/a
I'm confused, how can an unsteady and a steady simulation give the same answer ? For an unsteady simulation you have transient effects, pertubations in the flow etc which if averaged over enough time, MAY give you a similar result to a steady state simulation, but more by luck than anything else ? or is my understanding of steady and unsteady not correct ?? Bob
Sai Krishna likes this.
  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
What difference is betw. steady and unsteady simul matrix-1.0 FLUENT 3 August 5, 2007 11:30
using steady state results for unsteady flow siva appanna Main CFD Forum 3 February 20, 2006 06:29
Unsteady vs Steady simulation - any difference? Sally Main CFD Forum 16 December 16, 2005 10:15
steady or unsteady? (in dpm) winnie FLUENT 1 April 28, 2003 12:30
About the difference between steady and unsteady problems Lisa Main CFD Forum 11 July 5, 2000 15:37


All times are GMT -4. The time now is 18:29.