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-   -   Number of Timesteps and Physical Timescale (http://www.cfd-online.com/Forums/cfx/81085-number-timesteps-physical-timescale.html)

 Leuchte October 15, 2010 07:34

Number of Timesteps and Physical Timescale

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

 Josh October 15, 2010 07:54

http://www.cfd-online.com/Wiki/Ansys...gence_criteria

In Solver Control, you can choose to specify iterations, time, or timesteps.

 michael_owen October 15, 2010 10:27

Quote:
 Originally Posted by Leuchte (Post 279345) 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 October 15, 2010 10:28

Also, Josh, I think you are confusing the Analysis Type settings for transient with the Solver Control settings.

 Josh October 15, 2010 10:36

Indeed I am. 18-hour workdays fry your brain.

 michael_owen October 15, 2010 10:47

Been there.

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