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Old   November 9, 2005, 10:15
Default DPM and swirling flow
  #1
Vix
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Hello all.

I wonder if someone can help me? I am having problems with simulating a swirl burner that uses liquid fuel. I can simulate the flow just fine and I am able to get a recirculation zone in front of the burner as expected. The problem starts when I inject fuel droplets in the recirculation zone. My residuals go crazy, and no matter how big interval between the DPM iterations it doesn't normalize. I seem to be getting very large gas phase velocities in the same region.

I have tried smaller fuel droplets velocities, smaller under-relaxation factors for Discrete phase, but nothing works.

Has anyone had experience with that kind of problem?

Thanks in advance,

Vix
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Old   November 9, 2005, 10:36
Default Re: DPM and swirling flow
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RoM
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Try a small urf for density, density 0.5 and dpm 0.2 usually works fine. Do you have your own reaction kinectis?

RoM
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Old   November 10, 2005, 03:43
Default Re: DPM and swirling flow
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Vix
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Urf is under-relaxation factor right? OK, I'll try. I am not using reaction kinetics but equilibrium chemistry (PDF look-up tables)

Are you working on a similar problem?

ViX
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Old   November 10, 2005, 03:53
Default Re: DPM and swirling flow
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RoM
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If you use your own kinetics it could lead to numerical problems due to stiff chemistry but with equlibrium pdf this should not happen. I did some coal combustion recently and it worked well with underrelaxation 0.5 for density and 0.2 for dpm.

Good Luck, RoM
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Old   November 10, 2005, 05:28
Default Re: DPM and swirling flow
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Vix
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I seem to be getting a divergence even if I exclude reactions, just the interaction of discrete phase and continous phase is a problem.

Thanks for your advice!
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Old   November 11, 2005, 03:17
Default Re: DPM and swirling flow
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Wouter Harteveld
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Did you try a smaller particle mass flux? You may want to increase that in steps.
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Old   November 11, 2005, 05:56
Default Re: DPM and swirling flow
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Vix
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I am getting better results with a much lower mass flux, thanks, but still no convergence.

Could this also be a problem of the Lenght scale in the DPM panel? How does this affect residuals.

Vix

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Old   November 11, 2005, 06:33
Default Re: DPM and swirling flow
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RoM
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Sometimes fluent will calculate very large dpm concentrations, usually in the area of the dpm injections. You can use the adpat->iso value panel to calculate the max dpm concentration in your domain. If its close to your liquid fuel density (or even larger) you will get a problem with convergeance.

RoM
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Old   November 11, 2005, 08:37
Default Re: DPM and swirling flow
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Vix
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And how do I resolve this problem with a very high concentration?
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Old   November 11, 2005, 09:25
Default Re: DPM and swirling flow
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RoM
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There is no general solution to this problem. Your injection should enclose a large number of cells so the total mass flow is spilt. Dont use single injections or small group/cone injections for high mass flow rates. Use surface injections with fine surfaces meshes instead.

RoM
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Old   November 13, 2005, 06:46
Default Re: DPM and swirling flow
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Vix
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Thank you for your very helpful remarks and advice.

I' ll try to remesh my model and redistribute the DPM source and increase the number of particles in a group.

ViX
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Old   November 14, 2005, 04:51
Default Re: DPM and swirling flow
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Wouter Harteveld
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What also helped for me was to do 1 DPM iteration per continuous phase iteration (otherwise residuals oscilalte), and to create a decent initial velocity field by creating a gas velocity inlet with the spray droplet velocity at the same spot.
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