SST K-Omega Cubic constitutional relation

samsakcz · April 11, 2018, 18:05

Hi everyone, I have problem with Cubic constitutional relation when I do assymetric plane diffuser steady state sim. When I do the analysis with 'classical' SST K-Omega model (Linear relation) it converges fine, but when I change Linear constitutional relation with the Cubic one it starts diverge after few iterarions (with no dependence on the size or type of elemnts or the number of prism layers).

I use Star-CCM+ v12.02 with analysis saved here. That file is only one of 54 (different type or size of elemnts and different n° of prism layers) variants but all of them diverge at about 20th iteration.

Thank you very much for your advices.

ping · April 11, 2018, 22:26

more advanced turbulence and other physics settings will sometimes do this and you have several ways to improve things
.run a more basic setting - eg standard k-w for 100-200 iterations then change to the required and continue solving
.ramp up the under relaxation factors or cfl number over 50 to 100 iterations
.start in first order then change up after a while
.etc

April 11, 2018, 18:05	SST K-Omega Cubic constitutional relation	#1
samsakcz New Member Petr Šamša Join Date: Oct 2016 Posts: 2 Rep Power: 0	Hi everyone, I have problem with Cubic constitutional relation when I do assymetric plane diffuser steady state sim. When I do the analysis with 'classical' SST K-Omega model (Linear relation) it converges fine, but when I change Linear constitutional relation with the Cubic one it starts diverge after few iterarions (with no dependence on the size or type of elemnts or the number of prism layers). I use Star-CCM+ v12.02 with analysis saved here. That file is only one of 54 (different type or size of elemnts and different n° of prism layers) variants but all of them diverge at about 20th iteration. Thank you very much for your advices.

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April 11, 2018, 22:26		#2
ping Senior Member Ping Join Date: Mar 2009 Posts: 556 Rep Power: 20	more advanced turbulence and other physics settings will sometimes do this and you have several ways to improve things .run a more basic setting - eg standard k-w for 100-200 iterations then change to the required and continue solving .ramp up the under relaxation factors or cfl number over 50 to 100 iterations .start in first order then change up after a while .etc