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Old   July 1, 2012, 07:58
Default Convergence help
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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
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Old   July 1, 2012, 16:11
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Quote:
Originally Posted by kruno_88 View Post
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.
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