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-   -   Discretization Error vs Residual Error? (http://www.cfd-online.com/Forums/openfoam-solving/98865-discretization-error-vs-residual-error.html)

dancfd March 20, 2012 23:09

Discretization Error vs Residual Error?
 
Hello all,

I just ran a sensitivity study on my case to see if I could improve my accuracy by using SFCD (2nd order scheme for convection terms) vs linearUpwind (1st order accurate). All else being equal, the SFCD case had a p-residual of 5e-1 and the linearUpwind case had a p-residual of 10e-3. I expected better accuracy from the 2nd order accurate case, but the residuals appear to show that was not the case. I am running simpleFoam on a 2D airfoil. Could anyone please suggest why the residual is higher for the 2nd order scheme?

More strange behaviour: the SFCD took LESS time to execute the case, and resulted in values of Cd and Cm that were farther from the experimental data than the upwind scheme. I expected different. Can anyone explain this?

Thanks,

Dan

akidess March 21, 2012 03:49

I always thought linearUpwind is 2nd order upwind. Is plain "upwind" what you were intending to compare to?

dancfd March 26, 2012 20:05

Hello Anton,

Thanks for finding my error, I appreciate it.

Regards,
Dan


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