DPM convergence problem!

May 21, 2003, 23:01

Hi, everyone

It seems that coupled dpm calculation is very difficult to converge. The oscillation is kept during each dpm iteration. I have tried different mesh and lower the underrelaxation value, but there are no effects to dispear the divergence.

What should I do? It has confused me months. Any help will be greatly appreciated!!

Thank you!

Best regards

Winnie

ffsun · May 22, 2003, 05:38

I believe that a minimum of oscillation is unavoidable when using DPM.

But some of the parameters I use to ensure good results are:

Step length Injection frequency Spreading the injection a little (instead of a point injection)

Cheers

May 23, 2003, 05:39

Hi, Christian

Thank you for your replying!

Yes, I know that a smaller step length will decrease the integration time step and thus give a more accurate calculation, but it seems that when I lower the step length, the oscillation becomes a little unstable. So I follow a suggestion provided in this forum and choose the shortest length of my mesh as the step length.

And injection frequency seems appeared in unsteady calculation, I haven't find this parameter in my calculation. Does it have an effect in steady calculation??

The last one, "spread the injection a little". I have thought it, But I don't know how to realize it in my case. Because my injection condition is got from the experiment and in the experiment, the particles are injected from four locations with finite mass flow rates and the particle diameters are also known from experiment, if I change the injection number, the void fraction will also changed. Do you have any idea?

Thank you!!

Best regards

winnie

May 23, 2003, 08:16

Hi

Step length: I often use smaller steps than the cell size. This sometimes help removing unphysical DPM results. I dont know the effect on the oscillations

frequency: Sorry. I ment interaction with cont. phase.

Spread the injection: I just mean that sometimes it can be of advantage to inject into more than one cell. The calculation is not valid when the concentration is too high. So sometimes a surface injection can avoid "ugly" results compared to a point injection. But ofcause this is only an option if the design allows it. Maybe I have misunderstood you, but if you increase the number of injections, dont you then just decrease the mass flow accordingly to keep the total mass flow constant?

Cheers

May 23, 2003, 21:58

Hi, Christian

Thank you very much for your help.

I will try!

Regards

winnie

May 21, 2003, 23:01	DPM convergence problem!	#1
winnie Guest Posts: n/a	Hi, everyone It seems that coupled dpm calculation is very difficult to converge. The oscillation is kept during each dpm iteration. I have tried different mesh and lower the underrelaxation value, but there are no effects to dispear the divergence. What should I do? It has confused me months. Any help will be greatly appreciated!! Thank you! Best regards Winnie

May 22, 2003, 05:38	Re: DPM convergence problem!	#2
Christian Guest Posts: n/a	I believe that a minimum of oscillation is unavoidable when using DPM. But some of the parameters I use to ensure good results are: Step length Injection frequency Spreading the injection a little (instead of a point injection) Cheers ffsun likes this.

May 23, 2003, 05:39	Re: DPM convergence problem!	#3
winnie Guest Posts: n/a	Hi, Christian Thank you for your replying! Yes, I know that a smaller step length will decrease the integration time step and thus give a more accurate calculation, but it seems that when I lower the step length, the oscillation becomes a little unstable. So I follow a suggestion provided in this forum and choose the shortest length of my mesh as the step length. And injection frequency seems appeared in unsteady calculation, I haven't find this parameter in my calculation. Does it have an effect in steady calculation?? The last one, "spread the injection a little". I have thought it, But I don't know how to realize it in my case. Because my injection condition is got from the experiment and in the experiment, the particles are injected from four locations with finite mass flow rates and the particle diameters are also known from experiment, if I change the injection number, the void fraction will also changed. Do you have any idea? Thank you!! Best regards winnie

May 23, 2003, 08:16	Re: DPM convergence problem!	#4
Christian Guest Posts: n/a	Hi Step length: I often use smaller steps than the cell size. This sometimes help removing unphysical DPM results. I dont know the effect on the oscillations frequency: Sorry. I ment interaction with cont. phase. Spread the injection: I just mean that sometimes it can be of advantage to inject into more than one cell. The calculation is not valid when the concentration is too high. So sometimes a surface injection can avoid "ugly" results compared to a point injection. But ofcause this is only an option if the design allows it. Maybe I have misunderstood you, but if you increase the number of injections, dont you then just decrease the mass flow accordingly to keep the total mass flow constant? Cheers

May 23, 2003, 21:58	Re: DPM convergence problem!	#5
winnie Guest Posts: n/a	Hi, Christian Thank you very much for your help. I will try! Regards winnie

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