physical time scale && advection time

mortazavi · May 29, 2016, 23:04

Hi,
I am simulating steady state flow over a hydrofoil, but it doesn't converge to error less than 1e-4. I have read alot about the effects of time scale on the convergence, but still do'nt know how I can choose an appropriate physical time scale based on the advection time (reported at the end of out file). I mean is there any relationship between these parameters?
thanks,

eng_norouzi · May 29, 2016, 23:32

If you have no idea about the physical time scale for your problem, I think it's better to choose automatic time instead. it should be noted that sometimes bad mesh quality leads to high residuals and you cannot reduce them even by setting a very small timescale.

ghorrocks · May 30, 2016, 00:38

This FAQ covers it: http://www.cfd-online.com/Wiki/Ansys...gence_criteria

In your case as you have a free surface it is highly likely that a steady state result is not possible (or at least not easy) and you will have to run transient to get it to converge.

May 29, 2016, 23:04	physical time scale && advection time	#1
mortazavi Member SMN Join Date: Jun 2009 Location: CANADA Posts: 71 Rep Power: 16	Hi, I am simulating steady state flow over a hydrofoil, but it doesn't converge to error less than 1e-4. I have read alot about the effects of time scale on the convergence, but still do'nt know how I can choose an appropriate physical time scale based on the advection time (reported at the end of out file). I mean is there any relationship between these parameters? thanks,

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May 29, 2016, 23:32		#2
eng_norouzi Member ali Join Date: Feb 2011 Posts: 37 Rep Power: 15	If you have no idea about the physical time scale for your problem, I think it's better to choose automatic time instead. it should be noted that sometimes bad mesh quality leads to high residuals and you cannot reduce them even by setting a very small timescale.

May 30, 2016, 00:38		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	This FAQ covers it: http://www.cfd-online.com/Wiki/Ansys...gence_criteria In your case as you have a free surface it is highly likely that a steady state result is not possible (or at least not easy) and you will have to run transient to get it to converge.