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-   -   Convergence in solving energy source (http://www.cfd-online.com/Forums/fluent/77632-convergence-solving-energy-source.html)

 Floyd June 29, 2010 09:19

Convergence in solving energy source

Dear all,

I have set up a simple problem: a cylinder is a heat source which is placed in atmosphere under natural convection. I set it as transient state, density based solver. For the solution methods, I set the formulation as explicit and the other remained unchanged. I ran the case in a 0.05 time step, 15 iteration for each time step, and leaving the courant number, relaxation factors value default. I saw the residual is converging when iteration is started from 15 to 1, but the residual went up again when a new iteration is started for the next time step. The residual kept oscillating during the whole calculation and did not go to convergence. Does anyone here can tell me why this happened, please?

with thanks and regards,
Floyd

 mamad60 June 30, 2010 02:33

re

use pressure based solver with Presto Or body force weighted pressure discritization also try lowering momentum under relaxation factor to .3 and others between .8 to .5
use a smaller time step

 Floyd June 30, 2010 03:22

Hi Mohammd,

thanks for your suggestion, I followed your suggested setting in my case, the residual started from E-6 order but kept growing as a straight line, neither converge nor diverge. As I know, the pressure based solver is for incompressible flow, is it also applicable to solving natural convection heat transfer?

Thank you very much!
Floyd

 mamad60 July 4, 2010 09:10

re

dear Floyd
If you use bousinesseq approzimation in martial properties Fluent takes density constant everywhere except in Body Force term of natural convection
so you can user pressure based scheme
What is your rayleigh number in your case?

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