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

Number of Timesteps and Physical Timescale

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   October 15, 2010, 08:34
Default Number of Timesteps and Physical Timescale
  #1
New Member
 
Niklas
Join Date: Sep 2010
Posts: 7
Rep Power: 15
Leuchte is on a distinguished road
Hey,

sorry but i have to ask some very fundamental questions. The first question concerns the physical timescale. What advisements have to be done before i adjust this value?
The second question is: Were in Ansys can i adjust the number of timesteps?
Under Solver Control in Ansys-Pre, there is only a possibilty to adjust the number of maximum and minimum Iterations.
I´m using Ansys 12 in my Project.

regards
Nick
Leuchte is offline   Reply With Quote

Old   October 15, 2010, 08:54
Default
  #2
Senior Member
 
Joshua Counsil
Join Date: Jul 2009
Location: Halifax, Nova Scotia, Canada
Posts: 366
Rep Power: 17
Josh is on a distinguished road
For your first question:
http://www.cfd-online.com/Wiki/Ansys...gence_criteria

In Solver Control, you can choose to specify iterations, time, or timesteps.
Josh is offline   Reply With Quote

Old   October 15, 2010, 11:27
Default
  #3
Senior Member
 
Michael P. Owen
Join Date: Mar 2009
Posts: 196
Rep Power: 17
michael_owen is on a distinguished road
Quote:
Originally Posted by Leuchte View Post
Hey,

sorry but i have to ask some very fundamental questions. The first question concerns the physical timescale. What advisements have to be done before i adjust this value?
The second question is: Were in Ansys can i adjust the number of timesteps?
Under Solver Control in Ansys-Pre, there is only a possibilty to adjust the number of maximum and minimum Iterations.
I´m using Ansys 12 in my Project.

regards
Nick
It sounds like you are doing a steady state simulation. There are no "timesteps", there are only interations. The name "timescale" is somewhate confusing; CFX uses a false transient algorithm in steady state to under-relax the solution as it iterates towards convergence. That's why it's a time "scale" and not a time "step".

For your first question, a good choice is usually a fraction (a third for example) of a representative timescale in the problem, 1/omega for rotating machines, the residence time L/V for through flow problems, etc.
michael_owen is offline   Reply With Quote

Old   October 15, 2010, 11:28
Default
  #4
Senior Member
 
Michael P. Owen
Join Date: Mar 2009
Posts: 196
Rep Power: 17
michael_owen is on a distinguished road
Also, Josh, I think you are confusing the Analysis Type settings for transient with the Solver Control settings.
michael_owen is offline   Reply With Quote

Old   October 15, 2010, 11:36
Default
  #5
Senior Member
 
Joshua Counsil
Join Date: Jul 2009
Location: Halifax, Nova Scotia, Canada
Posts: 366
Rep Power: 17
Josh is on a distinguished road
Indeed I am. 18-hour workdays fry your brain.
Josh is offline   Reply With Quote

Old   October 15, 2010, 11:47
Default
  #6
Senior Member
 
Michael P. Owen
Join Date: Mar 2009
Posts: 196
Rep Power: 17
michael_owen is on a distinguished road
Been there.
michael_owen is offline   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
2 domains - 2 physical timesteps? How to? flattie CFX 5 April 5, 2009 20:27
physical velocity formulation and porous media KLG FLUENT 2 June 10, 2003 11:14
convergence problem A. Mohamed CFX 7 May 5, 2003 10:25


All times are GMT -4. The time now is 21:59.