Learning Forum

[scabo]

Hi,
I have few different particle diameters and I want to set the correct particle time step size equal to the particle relaxation time. So for smaller particles I need to reduce the time step. How do I control this using Fluent settings? I tried changing the step length factor/length scale. I calcualted the vel of particle from default settings and divided by an arbitray length scale to get the time step of choice. But there is some confusion. Can some let me know how can I change the particle time step size as I want? Lets say i want a particle time step size of 1e-5, how do I achieve it?

Also can i print the time step from the simulation?

thanks

[Rob]

It's a all particles setting, so you don't. Time step should show in the console when it's updated. 

[scabo]

Hi i didnt get. I have to set the particle time step using the length scale. Or i can use a udf right? How do i set a time step according to choice because different sized particle will have different time step.

And by console u mean when running locally? It does not show on hpc .out file.

[Rob]

If you have a range of particle sizes there is no one value (from reading your post) and Fluent has one time step as it's set at the DPM model, and not injection, level. 

Check the transcript if you're running remotely. If you mean in the DPM.out file, it's not available but the particle time is. 

[scabo]

I mean i am running particle diameters seperately. So i did length scale option but i think there is some issue thats why i want to explicitly mention the trajectory time step. How to do this?

No i mean the normal transcript of the run. Its not mentioned there.

[Rob]

I doubt it's available. You can try looking in header files and write a UDF, but I suspect it's not worth the effort. 

[scabo]

Okay then how can i know the part timestep the solver is using to check accuracy?

[Rob]

Increase/decrease Tracking Parameters. 

[scabo]

Yes but I can also use a UDF to give a specific time step for particles?