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-   -   convergence criteria (http://www.cfd-online.com/Forums/fluent/48059-convergence-criteria.html)

swarley April 27, 2008 07:51

convergence criteria
 
hi everyone,

i have a question about the convergence criteria. why does the criteria for momentum eqns and energy eguation differ? p.s: default for momentum 10-3, energy 10-7.

Angela April 27, 2008 22:30

Re: convergence criteria
 
I have also thought about this question. In my opinion, the convergence criteria of 10-3 is applied to both velosity and momentum is due to their definition. For momentum, the definition is mass*velocity. Bur for energy, the definition contains the item of square of velocity.I think that's why the convergence criteria of energy eqn should be 10-6,10-7.

Ramesh. K May 7, 2008 06:30

Re: convergence criteria
 
angela is partially correct. we have 3 equations to solve continutiy, momentum and energy equation. the order of the three equations are different so what we do is if we normalize the equations all will of the order of 1 so determining the convergence criteria depends upon whether the solver u solved is in normalized or not if normalized then convergence specified for all will be equal.

jpinho June 24, 2009 11:18

hi,
i am curious in this subject. im doing a standalone energy simulation with a heat flux boundary. The heat flux is very low, 1.25 mW, and the idea is to figure how long the solid will be under a specific temperature. ive done some calculations and this time is around 10 hours...

im having a problem because is not taking account on this 1.25mW each time step.. and im wondering if this can be because of the criteria convergence im using for energy..

if i run a simulation with a heat flux much greater, the solution converges with the theoretical formulas..

any suggestion?
thanks
jpinho


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