# Approach to simulate millions of particles in a room

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 January 29, 2020, 03:59 Approach to simulate millions of particles in a room #1 Member   MMatt Join Date: May 2013 Posts: 59 Rep Power: 9 I cannot decide which approach to use in order to simulate particles in a room. I've tried an Eulerian-Eulerian approach, but due to the number of particles (millions), it is not really computer efficient. I wanted to know if there was an other method I could use. Something maybe more statistical than deterministic. Such as in the video below (from 1min17): https://www.youtube.com/watch?v=qULwdb277Mc My aim is to see the particles concentration such as on the video. I don't need to see each particles, but their concentration in the fluid domain. Thank you!

 January 29, 2020, 04:22 Euler-Euler is statistical #2 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,948 Blog Entries: 1 Rep Power: 31 Hi Euler-Euler or Mixture models are statistical. Lagrangian on the other hand is a mix; it uses deterministic approach to predict the positions of parcels, however, each parcel represents multiple particles. There are at least two thing that you need to look at to decide if it is Euler-Euler (including PBM) or DPM that is more suitable. 1. Volume fraction of particles in the room. Less than 10-12%, you can use DPM and you should use DPM. More than that, you may use both but DPM would require additional collision model, such as DEM. 2. What's the objective of the simulation? __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

 January 29, 2020, 04:30 #3 Member   MMatt Join Date: May 2013 Posts: 59 Rep Power: 9 Hi, Thank you for your answer. Volume fraction is very very small (less than 1%), and what I'm interested to see is the evolution of the particles concentration in the fluid domain relative to time. Thanks!

 January 29, 2020, 04:31 DPM is the way to go #4 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,948 Blog Entries: 1 Rep Power: 31 Then use DPM. And calculate Stokes number. If it is less than 1, just use one-way coupling with fluid. MMatt likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

 January 29, 2020, 04:50 #5 Member   MMatt Join Date: May 2013 Posts: 59 Rep Power: 9 Thank you! However, two-way coupling is enabled by default and I cannot disable it (interaction with continuous phase).

 January 29, 2020, 04:54 #6 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,948 Blog Entries: 1 Rep Power: 31 Two-way coupling is always user's decision. You might have some other model enabled that requires two-way coupling, such as unsteady particle tracking. Do note that particle tracking is always unsteady because the equation has only one independent variable, time. Unsteady particle tracking is required when there is some unsteady phenomenon, such as coalscence or break-up, that need to be modeled. Otherwise, you can disable the Interaction. But do not disable it if St number is close to or greater than 1. MMatt likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

 January 30, 2020, 04:22 #7 Member   MMatt Join Date: May 2013 Posts: 59 Rep Power: 9 After more reading, I have noticed the Mixture model. However I am not sure if it would be appropriate to my case (my initial feeling is that it is not). I need to see particles accumulation in my fluid domain, therefore some of the particles could have a velocity of 0 or at least a very low velocity. Does that mean the Mixture model cannot be used? I know the question may sound stupid tho EDIT: Moreover, am I right in saying DPM would be more appropriate to my case than DDPM? The particle conccentration is very low (<1%). EDIT2: I do not need to simulate collision between particles, as their diameter is very small (sub 1um in diameter), therefore the particules could be considered as points, but they are NOT massless. If that makes any sense.

 January 30, 2020, 05:44 Mixture can be used but do not use #8 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,948 Blog Entries: 1 Rep Power: 31 Mixture model can be used but not very applicable, particularly when DPM is applicable. Since you wish to observe the accumulation, you have to simulate two-way coupled, Unsteady particle tracking otherwise you will not observe it. Use DPM; DDPM not required. MMatt likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

 January 30, 2020, 07:08 #9 Member   MMatt Join Date: May 2013 Posts: 59 Rep Power: 9 Thank you! One last question (didn't want to open a new thread), I cannot find the function to initialize the fluid domain with a defined number of particles. My plan was to implement them through an injection (a random concentration in the fluid domain is fine in my case, I just need the correct number of particles), but I've read there is a "volume injection" function (last message): https://studentcommunity.ansys.com/t...esidence-time/ However I cannot find it.

 January 30, 2020, 08:34 Beta feature #10 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,948 Blog Entries: 1 Rep Power: 31 Volume Injection is a beta feature. Enable it using def bfa yes Recommended would be to use File Injection. MMatt likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.