single phase boiling in a bottom heated dust

rezahemmat1985 · January 16, 2012, 02:55

Hi dears
I am simulation single phase boiling in a botoom heated rectangular duct via AVL FIRE software . I do the simulation with the software default's values for convergence criteria and under-relaxation factors . but the results devaiate alot with the experimental ones or it diverges . Please guide me how to use the suitable convergence criteria and under-relaxation factors to reach a logical and converge solution .
Thanks in advance

avlcfd · September 8, 2012, 03:21

Convergence critareia and under-relaxation factors are important but not the only and cruical factors for stability and accuracy. Strat with checking your physics e.g. initial and boundary conditions in general computational model setup for getting accurate results and good agreement with the measurement. With convergence criteria (if you are using the default one) you will influence on the accuracy and speed and with under-relaxation factors you will influence on speed-up of the simulation. Usually the values for convergence criteria of 1e-5 are a good choice for momentum and continuity equation. For under-relaxation factors the speed of convergency (and consequently the robustness) is influenced. For your case the value of 0.4 to 0.6 for momentum equation and 0.2 to 0.3 should be a good choice (without knowing more details of your problem it's conditions).

January 16, 2012, 02:55	single phase boiling in a bottom heated dust	#1
rezahemmat1985 New Member reza hemmat Join Date: Jan 2012 Posts: 24 Rep Power: 14	Hi dears I am simulation single phase boiling in a botoom heated rectangular duct via AVL FIRE software . I do the simulation with the software default's values for convergence criteria and under-relaxation factors . but the results devaiate alot with the experimental ones or it diverges . Please guide me how to use the suitable convergence criteria and under-relaxation factors to reach a logical and converge solution . Thanks in advance Last edited by rezahemmat1985; January 16, 2012 at 03:17.

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September 8, 2012, 03:21		#2
avlcfd New Member Maik SUFFA Join Date: Jul 2012 Posts: 7 Rep Power: 13	Convergence critareia and under-relaxation factors are important but not the only and cruical factors for stability and accuracy. Strat with checking your physics e.g. initial and boundary conditions in general computational model setup for getting accurate results and good agreement with the measurement. With convergence criteria (if you are using the default one) you will influence on the accuracy and speed and with under-relaxation factors you will influence on speed-up of the simulation. Usually the values for convergence criteria of 1e-5 are a good choice for momentum and continuity equation. For under-relaxation factors the speed of convergency (and consequently the robustness) is influenced. For your case the value of 0.4 to 0.6 for momentum equation and 0.2 to 0.3 should be a good choice (without knowing more details of your problem it's conditions).