[aiger]

Hi, I'm working with steady model, but in DPM unsteady particle tracking. I have paticle time step 0.001. How many time steps i must to set for 20 s.
In the Run Calculation how many number of iterations i must set?

[vinerm]

Number of time steps is ratio of the total time and time-step, so, 20/.001. But there is a catch here. The number of time-steps in Fluent's Unsteady Particle Tracking is meant for each DPM iteration. You wouldn't want particle to travel for 20 seconds in each DPM iteration because particles are affecting the flow. So, usually, you would want particle to cross at most one cell in every DPM iteration. Therefore, set the number of time-step to 5-10, maximum 20. This depends upon the particle velocity. if velocity is very high, reduce the particle time-step.

[aiger]

Thank you so much! Can I ask something else? But how do I know that it is 20 seconds? And what is the relation between number of iterations and number of particle time step? My particle velocity = 0.6 m/s.

[vinerm]

Iterations are for the Eulerian phase. They do not have any direct relation with the particles. Particle tracking is done after multiple iterations so as to give the flow to stabilize due to the source terms arising from the particle motion or other particle fields.

You can check the particle time by going to Particle Tracks and plotting it. However, what happens after particles have traveled for 20 s? If you want particles to disappear after that, then you have to use a UDF. If you just want to see what happens to particles within first 20 s, then you can run the simulation until most of the particles have traveled for 20 s and then plot the tracks with Filter on Residence Time. Filter option is available in Particle Tracking.