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ANJUM NAVEED May 27, 2006 14:22

question urgent
 
hi i m simulating gas cyclone with RNG k-e model using hedrahexal mesh. solution converge very fast except epsilon equation and then start to increase i m using default URF any suggestion. 2: what is relation between turbulent and flow equation. if i solve them separately i mean only simulating one of them at a time they both get converge very fast is this solution trust worthy. 3:what URF if i keep URF very low like .1 or .05 what effect it will have and solution will also right with these low urf thanks in advance Anjum

chankhar May 27, 2006 14:43

Re: question urgent
 
what is urf chankhar

Amr May 27, 2006 15:55

Re: question urgent
 
For part 2 of your question, and if you are on steady state, you can solve each of the equations (turbulence or flow) one at a time. This is when you first solve the flow, then turn the flow off, solve turbulence while flow is off, and finally, solve them together (some recommend that you use 2nd order discretization when you solve them together finally.

As for URF's, when they are low, the residues normally avoid instabilities and meanwhile, it takes longer time that the solution converge or residuals fall several orders of magnitude. Also try to use convergence indicators like mass or energy conservation (flux reports). Check Fluent guide for judging convergence in "using the solver section".

Cheers, Amr


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