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Old   September 8, 2014, 02:21
Default current position of particles
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mehrzad
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hello
I'm working with fluent dpm model for particle translation. I need to know the position of particles in domain. the dpm control panel for steady case provide the trajectory of particle. is there any way to get position of particles in domain without using UDF?
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Old   September 8, 2014, 10:16
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Hi Mehrzad,

If you are looking for particle positions in a steady state case - they don't exist, there is only the trajectories of particles. Only in transient flows you can get the particle positions. There, you can use calculation activities - export particle data to export the particle quantities of interest to certain software packages. This does not mean all these formats are easy to post-process in the sense of getting the numbers out for manipulation; if that is what you are looking at a UDF may be the way to go.

Good luck!
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Old   September 8, 2014, 11:07
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Quote:
Originally Posted by CeesH View Post
Hi Mehrzad,

If you are looking for particle positions in a steady state case - they don't exist, there is only the trajectories of particles. Only in transient flows you can get the particle positions. There, you can use calculation activities - export particle data to export the particle quantities of interest to certain software packages. This does not mean all these formats are easy to post-process in the sense of getting the numbers out for manipulation; if that is what you are looking at a UDF may be the way to go.

Good luck!
thank you Cees Haringa
in fluent user guide under dpm model section said it is possible to solve flow "steady" and treat particle "transiently". but until now i could not simulate particle transient while the flow solved in steady state. do you have any experience or idea how to do this?
and for udf I'vetried some but I've got some errors and working on it.
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Old   September 9, 2014, 05:42
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Hi Mehrzad,

That is indeed possible, unless you use a stirred tank geometry or something like that. But, if there are no moving parts in your domain, take the following approach:

To do unsteady (transient) particle tracking, you do have to enable the `transient' solver. In order to prevent FLUENT from recalculating the velocity field, disable the transport equations for momentum, turbulence, etc. in solution controls > equations.

Now, disable `interaction with continuous phase' (or do you want the momentum exchange with the particles to influence the flowfield? If so, you cannot use the approach outlined here) but do enable `unsteady particle tracking'. The flowfield will not change, but the particle tracking is transient.

Good luck!
Cees
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Old   September 9, 2014, 09:18
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Even if you are using steady particle tracking you can calculate the position of a given particle stream at a specific time, without using a udf. However, you will need to do some postprocessing outside of Fluent.
Save the particle data into a file format that you are familiar with. The data should include position and time for each of the streams. Then you you can determine the position of the particle stream or particle track at the time you are interested in.
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Old   September 9, 2014, 10:05
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Quote:
Originally Posted by CeesH View Post
Hi Mehrzad,

That is indeed possible, unless you use a stirred tank geometry or something like that. But, if there are no moving parts in your domain, take the following approach:

To do unsteady (transient) particle tracking, you do have to enable the `transient' solver. In order to prevent FLUENT from recalculating the velocity field, disable the transport equations for momentum, turbulence, etc. in solution controls > equations.

Now, disable `interaction with continuous phase' (or do you want the momentum exchange with the particles to influence the flowfield? If so, you cannot use the approach outlined here) but do enable `unsteady particle tracking'. The flowfield will not change, but the particle tracking is transient.

Good luck!
Cees
thank you very much Cees. it was very helpful. I have a question to be sure we are on the same page.
when I activate the transient solver and deactivate flow and turbulent eqs. for calculating dpm in "solution ->run calculation" there are boxes for time step of fluid and number of time step. is it necessary to change the time step here to the time step of particle and the number of time step to desired number for particle or not?
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Old   September 9, 2014, 10:10
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Quote:
Originally Posted by sescobar View Post
Even if you are using steady particle tracking you can calculate the position of a given particle stream at a specific time, without using a udf. However, you will need to do some postprocessing outside of Fluent.
Save the particle data into a file format that you are familiar with. The data should include position and time for each of the streams. Then you you can determine the position of the particle stream or particle track at the time you are interested in.
at the first this idea came to my mind but since the number of particle in the system is large the post processing would take a lot of time and effort. and for my final goal of this simulation i need to calculate particle locations transiently.
thank you for sharing your idea with me.
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Old   September 9, 2014, 10:34
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FLUENT does multiple particle-integration steps per timestep; it automatically tunes to the set accuracy I believe, but you may want to check the documentation for details on that.

In theory, this should mean you can take large timesteps if the number of sub-timestep particle position iterations in sufficient; but I have no experience with that (only with actual transient modeling); I'd advise taking a timestep that is not too large, maybe the time it requires for a particle to cross a gridcell or so. Number of timestep simply sets your flow timespan.

But indeed, the suggestion of Sescobar may work for you as well: if your geometry has an in- and outlet you get the trajectories, and knowing local velocity this gives you the position as well. Depends on what your eventual goal is if this suffices.
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Old   September 9, 2014, 12:16
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Quote:
Originally Posted by CeesH View Post
FLUENT does multiple particle-integration steps per timestep; it automatically tunes to the set accuracy I believe, but you may want to check the documentation for details on that.

In theory, this should mean you can take large timesteps if the number of sub-timestep particle position iterations in sufficient; but I have no experience with that (only with actual transient modeling); I'd advise taking a timestep that is not too large, maybe the time it requires for a particle to cross a gridcell or so. Number of timestep simply sets your flow timespan.

But indeed, the suggestion of Sescobar may work for you as well: if your geometry has an in- and outlet you get the trajectories, and knowing local velocity this gives you the position as well. Depends on what your eventual goal is if this suffices.
Thank you both Cees and Sescobar for your helpful answer. they helped me a lot .
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Old   September 9, 2014, 14:18
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hi everyone
Since this post is talking about DPM
and i'm working on simulation of bubble reactor and i didn't use DPM before , so can anyone help me with this if you have a guide or anything help me , i would be very thankful
thanks in advance
zain
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Old   September 11, 2014, 06:46
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Quote:
Originally Posted by CeesH View Post
FLUENT does multiple particle-integration steps per timestep; it automatically tunes to the set accuracy I believe, but you may want to check the documentation for details on that.

In theory, this should mean you can take large timesteps if the number of sub-timestep particle position iterations in sufficient; but I have no experience with that (only with actual transient modeling); I'd advise taking a timestep that is not too large, maybe the time it requires for a particle to cross a gridcell or so. Number of timestep simply sets your flow timespan.

But indeed, the suggestion of Sescobar may work for you as well: if your geometry has an in- and outlet you get the trajectories, and knowing local velocity this gives you the position as well. Depends on what your eventual goal is if this suffices.
dear Cees i want to inject particles into the domain for example every 0.2 sec but the time step for particle set to 0.003. in fluent injection panel you can choose between injecting particle at fluid time step or at particle time step. i set the time step for partile 0.003 and choose inject particle at fluid time step then in calculation menu i set the time step of flow 0.2 and when start calculation the calculation use the time step of flow instead of time step of particle. is there any way to fix this?
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Old   September 15, 2014, 12:11
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Dear mehrzad,

When you set "time step size" in the solution->run calculation panel, fluent will calculate you problem at that particular time-step.
And in you case if you are setting your fluid flow time step as 0.2 and for particles as 0.003 then fluent will inject (0.2/0.003)* (# of particles you are injecting at each time-step)

Hope you understand.
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Old   October 15, 2014, 02:32
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Quote:
Originally Posted by CeesH View Post
Hi Mehrzad,

That is indeed possible, unless you use a stirred tank geometry or something like that. But, if there are no moving parts in your domain, take the following approach:

To do unsteady (transient) particle tracking, you do have to enable the `transient' solver. In order to prevent FLUENT from recalculating the velocity field, disable the transport equations for momentum, turbulence, etc. in solution controls > equations.

Now, disable `interaction with continuous phase' (or do you want the momentum exchange with the particles to influence the flowfield? If so, you cannot use the approach outlined here) but do enable `unsteady particle tracking'. The flowfield will not change, but the particle tracking is transient.

Good luck!
Cees
Dear Cees I did what you've said in this post, and there is question no matter how many particle injected or tracked the calculation take a long time to complete. is that normal or not?
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Old   October 15, 2014, 02:40
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It can take a while, but should scale with the number of particles tracked. How many did you track exactly? And what do you consider to be a long time?
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Old   October 15, 2014, 04:35
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for example for injecting a single particle every 0.5 sec the calculation time is 1 min 55 sec in this case the number of particle are tracked is 4.
and for injecting 400 particles every 0.5 second calculation time is 2 min 7 sec, in this case the particle number tracked is 1640.
it seems no matter how many particle you tracked/inject it took the same time for same number of itteration.in both cases the iteration number was 50.
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Old   October 16, 2014, 02:04
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2 minutes for 50 iterations isn't that much is it?
But for some more information - are you running locally on a desktop or laptop, or on a computing cluster (I have bad experiences with the latter regarding particle tracking).

Do you have any other models that require some iterative calculations enabled?
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Old   October 16, 2014, 07:22
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Quote:
Originally Posted by CeesH View Post
2 minutes for 50 iterations isn't that much is it?
But for some more information - are you running locally on a desktop or laptop, or on a computing cluster (I have bad experiences with the latter regarding particle tracking).

Do you have any other models that require some iterative calculations enabled?
i know it's not too much but it does not depend on the number of tracked particle. i think 200 particle should take longer to track VS 1 particle. i run the calculation on desktop corei5 with 16 gig ram.
no just the flow which was solved in steady state with turbulence model and then as you said i disable the flow and turbulent Equation in "solution control" then run the particle in unsteady state.
is there any procedure to calculate particle unsteady while the flow is steady? i couldn't find the procedure you said in any FLUENT document/help file.
again Thank you for helping me.
I really appreciate everything you've done.
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Old   October 16, 2014, 08:00
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It could be that there is some `startup cost' due to the DPM model, which makes the simulations take a certain time independent of the number of particles. Then, the difference between 1 and 200 particles is so small that you hardly notice it. But believe me, once you track 1.000.000, you will notice a difference
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