CFD Online Discussion Forums

CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   FLUENT (https://www.cfd-online.com/Forums/fluent/)
-   -   Convergence help (https://www.cfd-online.com/Forums/fluent/104000-convergence-help.html)

kruno_88 July 1, 2012 07:58
Convergence help
 
Hi,

I'm running a steady flow simulations in Fluent. I'm using default settings for monitoring residuals (0,001) and my simulation convergates at 300 iterations and I get lift coefficient Cl around 4. I run same simulation again just put residuals to stop when decreased at 0,0001 and my solution convergates at 1600 iterations and I get lift coefficient around 8.... and I'm watchnig residuals diagram and in both simulations it looks good. From start it lineary goes down.

Can somebody please explain that big difference? I did that on few simulations and always get about doubled Cl.

Thanks

Jabba July 1, 2012 16:11
Quote:
Originally Posted by kruno_88 (Post 369100)
Hi,

I'm running a steady flow simulations in Fluent. I'm using default settings for monitoring residuals (0,001) and my simulation convergates at 300 iterations and I get lift coefficient Cl around 4. I run same simulation again just put residuals to stop when decreased at 0,0001 and my solution convergates at 1600 iterations and I get lift coefficient around 8.... and I'm watchnig residuals diagram and in both simulations it looks good. From start it lineary goes down.

Can somebody please explain that big difference? I did that on few simulations and always get about doubled Cl.

Thanks
Evaluating only the residuals is not sufficient to trully confirm the convergence of a calculation. You may define monitors to make sure your simualtion reaches a steady state.
In your case, it might be helpful to monitor metrics related to shear stress in the surfaces of interest, as well as lift and drag forces.


All times are GMT -4. The time now is 18:29.