CFD Review  
Serving the CFD Community with News, Articles, and Discussion
 
CFD Review

User Preferences
Site Sponsorship
Headline Feeds
Mobile Edition
Privacy Policy
Terms of Service
twitter

Submit a CFD Story

Site Sponsors
Siemens PLM Software
The Choice for CFD Meshing
Software Cradle

Tell a Friend
Help this site to grow by sending a friend an invitation to visit this site.

CFD News by Email
Did you know that you can get today's CFD Review headlines mailed to your inbox? Just log in and select Email Headlines Each Night on your User Preferences page.

 
Question: Are Local Timestep Methods Bad?
Posted Thu July 12, 2001 @09:00AM
Print version Email story Tweet story
Help Desk I've often wondered about the validity of attaining a steady-state solution with local time-stepping methods (aka CFL number). The problem to me seems that slowing the problem down in one area opposed to another would not yield a global steady-state solution - unless the simulation was run for a very long time even after the residuals have "converged". The residuals are small because the solution is balanced, but the transient processes are not necessarily in balance!

I know these methods are necessary and very useful for cases which have a large (several orders of magnitude) timescale variation, such as jets expanding into quiescent flow, but are the solutions really correct?


Azore CFD
Sponsor CFD Review

If you have really attained a steady-state solution with this method then you should be able to switch to a true global time step approach and take a large time step and see no difference in the solution (time derivatives are zero for steady state process). Problem is, I have seen solutions diverge and blow-up when performing this test of the "steady-state" solution.

My question to you is, how much do you trust solutions attained wtih local time-stepping methods. Do you worry about this phenomenon? Perhaps someone can prove that local time-stepping methods do achieve steady-state results for cases with large variation in timescale.

[ Post Comment ]

SGI Announces Flat Screen Display for Technical Professionals | Application: Benetton Formula 1 Using CFD to Design Cars  >

 

 
CFD Review Login
User name:

Password:

Create an Account

Related Links
  • More on Help Desk
  • Also by nwyman
  • This discussion has been archived. No new comments can be posted.

    He jests at scars who never felt a wound. -- Shakespeare, "Romeo and Juliet, II. 2" All content except comments
    ©2018, Viable Computing.

    [ home | submit story | search | polls | faq | preferences | privacy | terms of service | rss  ]