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-   -   Low Flow Convergence Help (http://www.cfd-online.com/Forums/fluent/111414-low-flow-convergence-help.html)

rypersaud January 6, 2013 14:10

Low Flow Convergence Help
 
2 Attachment(s)
Hey guys, need some help with convergence. The application involves a 3" inlet pipe with 52 m/s velocity discharged into a 26"X50" duct. The duct has a U-bend with a 20" outlet.

This is a very slow flow problem due to the large size of the duct. We are expecting the velocity at the outlet to be approximately 1 m/s.

Used a surface monitor plot at the outlet to look at the velocity, and scaled residuals criteria of 1e-5. The velocity of the outlet appears to have approached a value, however the residuals are quite high. I ran 5000 iterations to exclude the effect of under relaxation factors. I have posted the plots below.

Any suggestions, or direction on how to improve the model will be great. Thanks!

Attachment 18013

Attachment 18014

LuckyTran January 7, 2013 00:13

Seems like everything is okay except for residuals.

Have you tried a finer grid? What about discretization schemes, 2nd order upwind on all?

rypersaud January 7, 2013 11:23

I am using a student version of Fluent so I'm limited to 500000 cells and I'm using 2nd order for everything. I'm also using the Simple solver....would using another one help? any other ideas?

msaeedsadeghi January 7, 2013 23:59

It is better to use the simplest form (First Order).
It is obvious that the problem is with your mesh. Refine it and try to make a structured mesh.


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