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Sandeep Abhyankar December 8, 1999 10:35

Fluent Parallel/Serial version..jump in residuals
I have been encountering a rather strange problem while running Fluent 5.2.3 Parallel and Serial version. I have a case file which I am running using Fluent 5.2.3 Parallel version (using 2-CPU's ). The file runs fine and the residuals drop down smoothly. However when I save the case and data file and then continue to run these saved files further using a Serial 5.2.3 Fluent version, a sudden jump in the " continuity and the x,y,z vel residuals is seen in the residual plots...!!

I have seen this problem occur on win-nt, hp-unix and alpha-unix platforms. Any pointers as to why this might be happening ??

Thanks in advance.

Jonas Larsson December 9, 1999 05:39

Re: Fluent Parallel/Serial version..jump in residuals
I've seen similar things. I suspect that the numerics Fluent uses across partition boundaries is not exactly the same as in other regions. If you partition the case across many CPUs it is probably not possible to use the same "globally" implicit solver - the partition boundaries are probably treated in some explicit way. For very strongly swirling flows I have also sometimes had numercial problems across partition boundaries with "exploding" swirl velocites etc. Most often it converges to almost the same solution though.

Sandeep Abhyankar December 10, 1999 12:07

Re: Fluent Parallel/Serial version..jump in residuals
Thanks Jonas for your comments.

I had a talk with the tech support engineer at Fluent, and he told me that this has been reported as a bug in V5.2 and they have a fix for it in the next version.

Thanks anyways !

Jonas Larsson December 15, 1999 03:57

Re: Fluent Parallel/Serial version..jump in residuals
Heh, I have a feeling I've heard that one before ;-) 5.3 is out though, so you can test it yourself.

Sandeep Abhyankar January 10, 2000 10:57

Re: Fluent Parallel/Serial version..jump in residuals
Fluent tech support advised me that the bug regarding sudden jump in the residuals when you change from single to parallel processing has been fixed in Version 5.3 of Fluent.

However, I installed Version 5.3.18 recenlty, and I continue to see the same erroneous behavior.

Wonder if the bug was really fixed..!

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