Imbalances

Zaktatir · November 2, 2011, 05:19

I found out that uncontrolled big imbalances (continuity or momentum equations) may lead to physical instability and therefore for example to another flow regime (especially in multiphase flow-parallel computing).

Can anyone agree to that or tell me about such an experience.

Jessica

ghorrocks · November 2, 2011, 20:55

Yes, if a simulation is far from converged, or even worse diverging, the results could be anything. Including being in completely the wrong flow regime.

Zaktatir · November 3, 2011, 02:19

Yes i agree. Nevertheless for mass transfer or heat transfer it will be hard to stay under 1% for the conservation target...

ghorrocks · November 3, 2011, 03:57

Some simulations are hard to get the imbalances to converge. Often these are simulations with big variations in time scales - the short time scales are converged but the longer time scales take lots of iterations to converge.

Zaktatir · November 3, 2011, 04:08

yes in fact, the simulation will be expensive.

ghorrocks · November 3, 2011, 05:22

That's right. Simulations with a large range of any scale are difficult - length (very big sections going to very small sections), time (long and short time constants), or anything else.

Zaktatir · November 3, 2011, 07:40

It was irritating me the fact that even the support did not know or gin out the problem, it is clear that numerical imbalance lead to physical insatiability but i have not thought that it artifacts the results dramatically.

Now i am trying to build new accurate test case

November 2, 2011, 05:19	Imbalances	#1
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	I found out that uncontrolled big imbalances (continuity or momentum equations) may lead to physical instability and therefore for example to another flow regime (especially in multiphase flow-parallel computing). Can anyone agree to that or tell me about such an experience. Jessica

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November 2, 2011, 20:55		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Yes, if a simulation is far from converged, or even worse diverging, the results could be anything. Including being in completely the wrong flow regime.

November 3, 2011, 02:19		#3
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	Yes i agree. Nevertheless for mass transfer or heat transfer it will be hard to stay under 1% for the conservation target...

November 3, 2011, 03:57		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Some simulations are hard to get the imbalances to converge. Often these are simulations with big variations in time scales - the short time scales are converged but the longer time scales take lots of iterations to converge.

November 3, 2011, 04:08		#5
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	yes in fact, the simulation will be expensive.

November 3, 2011, 05:22		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	That's right. Simulations with a large range of any scale are difficult - length (very big sections going to very small sections), time (long and short time constants), or anything else.

November 3, 2011, 07:40		#7
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	It was irritating me the fact that even the support did not know or gin out the problem, it is clear that numerical imbalance lead to physical insatiability but i have not thought that it artifacts the results dramatically. Now i am trying to build new accurate test case