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-   -   Need help on my CFD homework. RMS fluctuates. (http://www.cfd-online.com/Forums/cfx/105368-need-help-my-cfd-homework-rms-fluctuates.html)

Anna Tian July 28, 2012 17:52

Need help on my CFD homework. RMS fluctuates.
 
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Hello everyone,

I simulated a case by CFX-solver. But the RMS value does not converge. The mesh quality is above 0.5 at ICEM. I set the timestep very small to 0.001s. (Initially it was larger, but there's still RMS fluctuation for nearly every timestep.) I copied the boundary condition setting from my classmate. It's not likely to have any problem at it. Since I'm not allowed to distribute our homework, I can only upload my CFX-solver pictures. Hope you can give me some hints about where the problem might be. :confused:

ghorrocks July 29, 2012 07:24

This question is a FAQ: http://www.cfd-online.com/Wiki/Ansys...gence_criteria

As the residuals do not oscillate it is unlikely to be transient flow. Much more likely mesh quality (ie remesh with better quality mesh) or numerical precision (ie try double precision).


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