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Convergence issue - combustion and wall heat transfer |
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October 9, 2014, 10:14 |
Convergence issue - combustion and wall heat transfer
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#1 |
Member
Join Date: Aug 2011
Posts: 89
Rep Power: 15 |
Combustion community,
I am having a really troubling problem. I am simulating combustion in Fluent using the non-premixed model. I have two inlets fuel streams and a single oxidizer stream. When I model the combustion, I get spikes in my turbulence and continuity residuals every 10-20 iterations, but the outlet temperature converges well and the heat flux balance at the end of the run is close to zero. Then I add in a heat flux through the walls, using an exterior heat transfer coefficient and bulk temperature. Once this happens, the outlet temperature has swings of up to 100 degrees C and the heat balance way off balance. I have been working this model for days (long, 12+ hour days) with almost no progress. Has anyone seen this, or have any ideas why this might be occurring? ANY ideas are welcome! I have added some plots of outlet temperature fluctuations and residuals Last edited by MachZero; October 9, 2014 at 10:24. Reason: Added pictures |
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October 9, 2014, 14:32 |
update
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#2 |
Member
Join Date: Aug 2011
Posts: 89
Rep Power: 15 |
Update,
I was using the pseudotransient solver with low URFs on a poly mesh. I have seen to get a more consistent outlet temperature with a segregated solver, but the convergence is pretty poor when looking at residuals. There are a lot of spikes. |
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October 11, 2014, 13:52 |
reply
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#3 |
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Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 65
Rep Power: 14 |
I would contact support...
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October 11, 2014, 14:32 |
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#4 |
Senior Member
François Grégoire
Join Date: Jan 2010
Location: Canada
Posts: 392
Rep Power: 17 |
No so fast on the support, lots of details are missing.
As a first guess, I think mesh and timestep can have a big influence on your case : 1. Ask on the ANSYS Meshing & Geometry forum how you could make a structured mesh. and/or 2. Reduce the timestep and see if it affects the oscillations. |
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Tags |
combustion modelling, convection heat flux, convergence issues, heat transfer balance, turbulence modeling |
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