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-   -   Validity of Local Time Scale Factor (http://www.cfd-online.com/Forums/cfx/74191-validity-local-time-scale-factor.html)

kuhbuh March 26, 2010 04:59

Validity of Local Time Scale Factor
 
Hi everyone!

I'm modeling a mixing process of high speed and slow speed fluids (ratio of 20:1). I often get good convergence using time scale factor which is I think more appropriate in my case because of the difference in velocities. However, Sir Glenn and Sir Robin and others have recommended in this forum that such case should be run again using physical time scale but I usually end up having fluctuating residuals if I do this. In ANYS12 Manual, there is still no mention of "unreliable" solution using local time scale factor. Is it really "unreliable"?


Thank you,
kuh

ghorrocks March 26, 2010 06:10

Yes, it can be unreliable. So yes, you really need to run the last 10 iterations or so using physical timescale so the flow time scales can be sorted out. Note you can do this as the simulation progresses so no need to stop and restart (with edit run in progress).

I don't get called sir very often :)

pavitran March 26, 2010 09:32

Hi
 
Quote:

Originally Posted by ghorrocks (Post 251793)
Yes, it can be unreliable. So yes, you really need to run the last 10 iterations or so using physical timescale so the flow time scales can be sorted out. Note you can do this as the simulation progresses so no need to stop and restart (with edit run in progress).
I don't get called sir very often :)

1. When you say that it is unreliable, I would like to understand, why does a steady state simulation result depends on the time scale that we choose?

kuhbuh March 26, 2010 09:36

Thank you very much Sir Glenn for your urgent response. I didn't know that we can "delete a parameter" from the edit run in progress option. I think "Sir" is just appropriate since you have our source of knowledge for many years now. Thanks again.

ghorrocks March 26, 2010 16:15

Quote:

When you say that it is unreliable, I would like to understand
Have a look at this post by Sir Robin (who sadly got banished from this forum years ago):
http://www.cfd-online.com/Forums/cfx...le-factor.html


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