why interDyMFoam does not support backward ddt scheme?

Yage · March 3, 2016, 05:02

Dear Foamer,

I would like to use backward second order time discretization in interDyMFoam, but the solver doest not support this time scheme.

Could someone explain the reason for that?

Many Thanks,
Yage

Yage · March 3, 2016, 05:31

I found that the interDyMFoam support Crank-Nicolson (CN) scheme and I set the weighing factor to 1 for fully second order accuracy.

But the alphasubcycle must be 1 in this case.

Any idea about the reason?

olivierG · March 3, 2016, 06:53

hello,

This may come from the fact the backward are not a bounded scheme, and MULES need it, or that MULES aren't coded to use backward.
CN just need current and old time, so sub-cycling used in MULES may not be usable. Same for backward.

regards,
olivier

Yage · March 3, 2016, 08:16

Quote:

Originally Posted by olivierG

hello,

This may come from the fact the backward are not a bounded scheme, and MULES need it, or that MULES aren't coded to use backward.
CN just need current and old time, so sub-cycling used in MULES may not be usable. Same for backward.

regards,
olivier

Thanks for your answear

Yage · March 3, 2016, 08:18

Quote:

Originally Posted by olivierG

hello,

This may come from the fact the backward are not a bounded scheme, and MULES need it, or that MULES aren't coded to use backward.
CN just need current and old time, so sub-cycling used in MULES may not be usable. Same for backward.

regards,
olivier

and any suggestion for which one to use, 1st order ddt + sub-cycling or 2nd order ddt without sub-cycling?

Regards,
Yage

olivierG · March 3, 2016, 09:26

hello,

I would say first order for a RANS may be enough, and 2nd order with lower time step for more fine RANS/ LES case.

regards,
olivier

Yage · March 3, 2016, 13:47

Quote:

Originally Posted by olivierG

hello,

I would say first order for a RANS may be enough, and 2nd order with lower time step for more fine RANS/ LES case.

regards,
olivier

Thanks for the suggestion

March 3, 2016, 05:02	why interDyMFoam does not support backward ddt scheme?	#1
Yage Member Yage Join Date: May 2014 Posts: 60 Rep Power: 12	Dear Foamer, I would like to use backward second order time discretization in interDyMFoam, but the solver doest not support this time scheme. Could someone explain the reason for that? Many Thanks, Yage

March 3, 2016, 06:53		#3
olivierG Senior Member Olivier Join Date: Jun 2009 Location: France, grenoble Posts: 272 Rep Power: 18	hello, This may come from the fact the backward are not a bounded scheme, and MULES need it, or that MULES aren't coded to use backward. CN just need current and old time, so sub-cycling used in MULES may not be usable. Same for backward. regards, olivier Yage, aow, Turin Turambar and 2 others like this.

March 3, 2016, 09:26		#6
olivierG Senior Member Olivier Join Date: Jun 2009 Location: France, grenoble Posts: 272 Rep Power: 18	hello, I would say first order for a RANS may be enough, and 2nd order with lower time step for more fine RANS/ LES case. regards, olivier Richal Sun likes this.

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March 3, 2016, 05:31		#2
Yage Member Yage Join Date: May 2014 Posts: 60 Rep Power: 12	I found that the interDyMFoam support Crank-Nicolson (CN) scheme and I set the weighing factor to 1 for fully second order accuracy. But the alphasubcycle must be 1 in this case. Any idea about the reason?