Learning Forum

[kiran.purushothamakeshavan]

Hi,
I used a UDF to count the particles that hit a wall. I save the particle ID's using p-> part_id;
I see that there is a lot of repeating ID's from the data that I export.
My question is why am I seeing number/ ID's that repeat? I have posted an example of the id numbers of these particles.

I have more examples below and the particles when sorted show 4 id's of the same number then it changes to a new number.

 

 

[Rob]

What is the DPM wall setting? 

[kiran.purushothamakeshavan]

This is a custom DPM BC, I used a UDF.
Under certain condition the particle sticks (Particle ID is written into a text file) and then the path is aborted.

[Rob]

You shouldn't see repeats if the particle isn't bouncing. Are you running single or multiple nodes Fluent?

[kiran.purushothamakeshavan]

I’m not sure what you mean by this. I ran the simulation using 4 or 6 processor cores (not sure exactly how many processors I used).

When I run it with 6 processors I still see that the particle ID’s repeat for approximately 4 times in the text file. Do you think I must only count one particle ID once rather than take the sum of all these id’s?

This is what I see when I go to parallel> network> bandwidth

 

[Rob]

And when you run on one processor?

[kiran.purushothamakeshavan]

 

I ran it with 1 processor, and I still see 4 ID’s which repeat.

 

I have attached my DPM setting, I made sure I have disabled reinjection.

[Rob]

Does the UDF tag the particle as trapped and then abort? Is there a way for a particle to be tagged to the file, but not by the kill rule?

[kiran.purushothamakeshavan]

From the manual what I see is that if I use PATH_ABORT fluent understands it as particle trapped.

[Rob]

It does, but check the reporting function is also triggering PATH_ABORT instantly. 

[kiran.purushothamakeshavan]

 

What do you mean by checking the reporting functions which are triggered?

 

[Rob]

If you trigger the report does it instantly trigger the PATH_ABORT or is there another particle integration step before the PATH_ABORT?

[kiran.purushothamakeshavan]

No there is no particle integration time step before the particle aborts.

Interesting thing to note is that my DPM summary is as follows:

This is my DPM settings:

From one of your article I found the relationship between number of parcels and number of particles:

Multiphase Flows: All Categories>Fluids - Multiphase Flows>How are number of particles per parcel calculated for unsteady DPM simulations?

From this what I understand is that I would release 20 particles (because form the ecxcel sheet, #particles/ parcel ~ 1 and number of stream = 20) every 0.01s, so for the entirity of the simulation I would have 20*200 particles for 2 seconds. 

Instead, from my PATH_ABORT section of my UDF, I get this repeating particle ID's:

Why do I see So many particles with repeating ID's and varied values of particle velocity at imoact with the custom wall?

I hope the question is clear.

Thanks,
Kiran

[Rob]

Having spoken to DEV the parcel IDs are supposed to be unique but may not be under certain circumstances. Please review the release notes when 25R1 becomes available. 

[kiran.purushothamakeshavan]

Hello,

I tried checking for the particle tracks> reporting> summary, gives me the total particles in the system as follows:

This gives me a proper estimate for the number of particles in the domain while my text file gives me a total of 12761 rows of particle ID's (most of them are repeating).

But when I check for the number of unique particle ID's from the data I get from the text file. I see that the number of particles =3400.

Why is this happening?

Thanks,
Kiran 

[Rob]

So the unique IDs tie up with the Fluent report? 

[kiran.purushothamakeshavan]

 

Yes.

But each repeated ID gives me atleast one variation of the velocity values. It’s just confusing why this happens.

 

Do you think I must just stick to using the unique particle ID’s and velocities for my calculations?

Thanks,
Kiran

 

[Rob]

Hence checking parallel and integration steps post report & pre-Abort.  And my comments re 25R1.