Learning Forum

[Atlas8818]

Hi!

I'm running DPM model to simulate the process of dust discharge,but if I choose the "Interaction with Continuous Phase ",It's going to diverge. Also,if it doesn't diverge,there are always many particles "escaped".Here are my settings,can someone help me?

DPM settings.pdf

[Atlas8818]

Every time I choose the "Interaction with Continuous Phase" , the result always like this and later to diverge.

[Rob]

How much dust are you adding into the domain? How well resolved is the flow? Divergence can be caused by many factors, and whilst the DPM model is causing it, you may find the DPM model isn't to blame.

[Atlas8818]

Hi Bob´╝îthanks for your answer ´╝îI set the dust flow rate to 0.1 kg/s ´╝îand the stop time is 0.05s .When the "Interaction with Continuous Phase " is not be chosen with the same settings ´╝îthe result is wonderful ´╝îlike this figure.

But when I choose the "Interaction with Continuous Phase "´╝îIt's either diverging´╝îor a lot of particles are escaping. The second picture is just after the initial injection ´╝îand the third is the result after a large number of particles escaping. I'm really confused that why there are so many particles being like this.Can you help me?

Yours´╝îsincerely .

[Atlas8818]

By the way ´╝îmy container is an airtight container with only an inlet and no outlet.

[Rob]

So no other flow, it's just a continuous injection of dust? If that's the case, how are particles escaping?

[Atlas8818]

Yes´╝îI just set the injection of dust´╝îthat's why I think maybe it's because of DPM model. Actually I'm not really know how the particle escaing´╝îbut the contours are here. The first one has particles escaping´╝îand the second one doesn't.

[Rob]

Check the boundary condition settings, you may have changed something you didn't mean to. Looking at the second image you also need to think about the particle accumulation, read up on the DPM model to see how it works. The convergence is very likely a result of the particle motion and concentration.

[Amine Ben Hadj Ali]

Might reduce time step or dpm URF.

[Atlas8818]

Thank you´╝îsir. I try to check my boundary conditions and read the manual´╝îbut I still can't to solve it.Even I stop the injection and just let it run itself´╝î the particles have already escaped nearly almost. However´╝îmy model doesn't have a outlet´╝îso the particle eacsping is not right.

[Atlas8818]

I have tried to reduce the dpm URF to 0.01´╝îbut it doen't help to stop the particles to escaping. Actually the particle is nearly to be zero.

[Rob]

Particles can only escape if a boundary is set to escape, otherwise they eventually go "incomplete" or "abort" if they run out of tracking steps or get lost by the solver. URF won't alter this, it'll only make the solver take longer to converge whilst being more stable.

[Amine Ben Hadj Ali]

Verify the DPM B.C you are using: pretty sure the particles are injected and right away escaping meaning the injection direction is wrong.

[Atlas8818]

You are right´╝îsir. When I set the "inlet" to reflect´╝îthe particles don't be escaped. However´╝îI'm facing a new question that the simulation is never convergent.

[Atlas8818]

Thank you´╝îDrAmine. I have tried to check my injection direction and found the particles don't be escaped when I set the "inlet" to reflect . Unfortunately´╝îwith the particles not being escaped´╝îmy consult is terrible. It doesn't converge anymore.

[Amine Ben Hadj Ali]

'Check the injection direction or inject the particles at your inlet with direction being normal. Provide a starting velocity for them.

[Atlas8818]

Actually my injection direction is from inlet with its direction being normal.And I also set the inlet to be a velocity-inlet with 0.98m/s.But it always have more than a third parcels escaping.

[Amine Ben Hadj Ali]

Check the velocity field if it is massively affecting the particle tracks.

[Atlas8818]

You are right! It's very kind of you! Thank you so much!! Now my question has solved!

[Atlas8818]

Oh my god´╝îI'm so sad to find it's converge because of the lower URF. When I turn the URF to 0.1´╝îit's still diverge and also having particles escaping.

[Amine Ben Hadj Ali]

URF of what?

[Atlas8818]

I set the URF of DPMÒÇüenergy and momentum to 0.01 and run 120 ms. The result is very well. But when I turn them to 0.5´╝îit's still diverge.

[Amine Ben Hadj Ali]

That means you require better to reduce the time steps of particle/Flow. DPM URF can be reduced but you then need to run a couple of dpm sources updates every time step to get 100% load at the end (okay this requirement has been alleviated thanks to some smart algorithms). What about increasing the number of particle streams? That will smooth out the sources :)

[Atlas8818]

I'm so grateful to receive your answer´╝îyou are so patient to help me. Nothing can express my gratitude to you.
I tried to reduce the particle time step´╝îand I also turn down the flow time step. But it do little help to convergence.
I had increased the number of particle streams´╝îit did help to convergence but caused a lot of particles escaping so that the result were not accurate.

[Amine Ben Hadj Ali]

there is no harm in having a lot of particles escaping if this is realistic. Please check if the boundary conditions you are using are making a sense and if yes, I need to apologize as I cannot do more than providing this blind guidance at this stage

[Atlas8818]

Thank you very much for your advice, I will continue to try, wish me success!

[Amine Ben Hadj Ali]

Welcome and good luck!