convergence of the solution

amar · July 3, 2009, 08:33

Dear all

I'd like to know what is the criteria to be sure that my solution is really converged.

thanks a lot

-mAx- · July 3, 2009, 08:45

If you have a goal, then monitor it (force, pressure at inlet , massflow rate, etc..).
You achieve convergence if the monitoring doesn't fluctuate anymore with iterations

Monker1980 · July 5, 2009, 09:08

Convergence criteria are very problem dependent. My usual approach is to monitor a variety of variables (e.g. velocity at several points, forces on the body, mass flow rates) - the more the better really. As -mAx- says, once the values of these have stabilised then you have a converged solution. BUT only IF your residuals have fallen by a suitable amount from their initial values (don't rely on Fluent's default 10e-3 convergence criteria). What is a suitable amount? Again, very problem dependent, but for a steady-state external aerodynamics type problem I would expect the continuity residual to drop below 10e-6 and the velocity (momentum) residuals to drop much lower than that. The Fluent user guide has some helpful guidance on this too.

July 3, 2009, 08:33	convergence of the solution	#1
amar Member amar Join Date: Mar 2009 Posts: 31 Rep Power: 17	Dear all I'd like to know what is the criteria to be sure that my solution is really converged. thanks a lot

July 3, 2009, 08:45		#2
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	If you have a goal, then monitor it (force, pressure at inlet , massflow rate, etc..). You achieve convergence if the monitoring doesn't fluctuate anymore with iterations __________________ In memory of my friend Hervé: CFD engineer & freerider

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July 5, 2009, 09:08		#3
Monker1980 New Member Join Date: Jul 2009 Posts: 7 Rep Power: 16	Convergence criteria are very problem dependent. My usual approach is to monitor a variety of variables (e.g. velocity at several points, forces on the body, mass flow rates) - the more the better really. As -mAx- says, once the values of these have stabilised then you have a converged solution. BUT only IF your residuals have fallen by a suitable amount from their initial values (don't rely on Fluent's default 10e-3 convergence criteria). What is a suitable amount? Again, very problem dependent, but for a steady-state external aerodynamics type problem I would expect the continuity residual to drop below 10e-6 and the velocity (momentum) residuals to drop much lower than that. The Fluent user guide has some helpful guidance on this too.