A question about discristization scheme

lehoanganh07 · October 13, 2014, 11:08

Hello,
I read several topics about this problem but still not clearly. Yes, It is known that second order give more accurate result than first order scheme. But, in my case, cavitating flow, many researcher only used second order for pressure and momentum equations, for other equations just first order scheme and the result was good to compare to experimental result. The other used second order for all equations and also gave good result.
For me, when I use the same way as second order only for momentum and pressure equation the results sre good to compare to my experiment. But with all equation are second order, the length of cavity is different.
Also the same question for time scheme. Fluent said that first order implicit time is good for almost situations. In my case, first order time also gave good result than second order time.
So I am not really clear which one is better and I think this also help someone else. Could you share your experience on this kind of problem!!

ghost82 · October 13, 2014, 11:16

Hi,
second order schemes are more accurate.
Usually cavitating flows are difficult to converge, expecially the vapour equation, and this is the reason for the choice of the first upwind scheme, which is easier to converge.
So, if you can converge with second order schemes, go for them, if you have trouble to reach convergence switch to first order.

lehoanganh07 · October 13, 2014, 11:32

Thank you, ghost82
How about time implicit scheme: first and second order implicit. Also same reason?

ghost82 · October 13, 2014, 11:33

As far as I know, yes.

October 13, 2014, 11:08	A question about discristization scheme	#1
lehoanganh07 Member le hoang anh Join Date: Oct 2012 Posts: 96 Rep Power: 13	Hello, I read several topics about this problem but still not clearly. Yes, It is known that second order give more accurate result than first order scheme. But, in my case, cavitating flow, many researcher only used second order for pressure and momentum equations, for other equations just first order scheme and the result was good to compare to experimental result. The other used second order for all equations and also gave good result. For me, when I use the same way as second order only for momentum and pressure equation the results sre good to compare to my experiment. But with all equation are second order, the length of cavity is different. Also the same question for time scheme. Fluent said that first order implicit time is good for almost situations. In my case, first order time also gave good result than second order time. So I am not really clear which one is better and I think this also help someone else. Could you share your experience on this kind of problem!!

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October 13, 2014, 11:16		#2
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 26	Hi, second order schemes are more accurate. Usually cavitating flows are difficult to converge, expecially the vapour equation, and this is the reason for the choice of the first upwind scheme, which is easier to converge. So, if you can converge with second order schemes, go for them, if you have trouble to reach convergence switch to first order.

October 13, 2014, 11:32		#3
lehoanganh07 Member le hoang anh Join Date: Oct 2012 Posts: 96 Rep Power: 13	Thank you, ghost82 How about time implicit scheme: first and second order implicit. Also same reason?

October 13, 2014, 11:33		#4
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 26	As far as I know, yes.