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Laika January 20, 2006 05:06

DPM; particle seeded / deleted by UDF
Dear Fluent Users,

To model what I need to model, I need to develop a UDF that generates particles in a simulation using Discrete Phase Model. It should be able to delete them as well.

Under certain conditions in my transient simulation, there will be particles in my flow, that actually behave like particles. Like a kind of condensation cores jumping into existance when the conditions are right, and then acting as a species source (either positive or negative) for the gaseous phase. When the conditions are right, these particles can dissapear as well.

So part of the UDF should be able to bring particles into existance. But I don't see a possibility to do this. How can I create a particle for the DPM in the middle of the flow field at a priory unknown locations.

One idea I have, but I don't know whether this will work: can I create a file-injection, and have an execute_at_end UDF modify the injection-file on the fly? Will Fluent actually reread the file every time step? It's just an idea. Anyone who tried this kind of things?

other suggestions?

thanks in advance,

Laika, still orbiting

HS January 20, 2006 06:54

Re: DPM; particle seeded / deleted by UDF
I think the easiest way to remove particles is to set their flowrate to zero (from a UDF). FLUENT will remove such particles at the end of each time step automatically.

Considering the injection, I suggest you setup a single or group type injection and then write a UDF to associate with the injection. The UDF can set the flowrate for the injection to zero at all times unless it is time to create a parcel. It can then change the position from the UDF so that what is set in the Injections-dialouge doesn't matter.

I have not done this exactly, but something a bit similar, and I think you could get that approach to work. Maybe there is some smarter way to do it. I would be very interested if that was the case! :)


Laika January 20, 2006 08:01

Re: DPM; particle seeded / deleted by UDF
OK for the removal! Thanks

For the injection: that's a clever idea. So you suggest I make somewere an injection of fresh zero-flow rate particles. As soon as I need particles to be generated anywere in my model, I take a 'fresh' particle, change it's position through the UDF and give it a real flow rate in order to keep it 'alive'.

Have I clearly understood your suggestion?

thanks! Laika, still orbiting

HS January 20, 2006 09:05

Re: DPM; particle seeded / deleted by UDF
Yes, that was almost exactly what I meant! Only make sure you have a positive flow-rate specified in the Injection-setup, otherwise FLUENT will not care about the injection at all in the first place. The UDF shall then change the flowrate to zero all the time except when you need the particle(s), and then also change the position, velocities etc.

Good luck!


Laika January 20, 2006 09:20

Re: DPM; particle seeded / deleted by UDF
Thanks a lot! Great idea!

I'll let you know if it works...

cheers, Laika, still orbiting

HS January 20, 2006 10:32

Re: DPM; particle seeded / deleted by UDF
Yes please let me know if it does! I would be very interested. Once again good luck!

MANOJKUMAR January 23, 2006 00:40

Re: DPM; particle seeded / deleted by UDF
Hello Laika Can u suggeted to make UDF for injection setting. I also doing the same type of problem.I doing on the combustion model and light diesel oil used as fuel and for combustion i try do do with injection. I try with doing injection but not getting result so please give me the direction for making UDF for DPM. Thanks, Manojkumar

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