Learning Forum

[lochihsiu]

Hi

I have a project regarding particles dispersion. Lately, I found something strange in Fluent DPM. I did a test by injecting a particle at constant speed and zero drag coefficient. So, the particle should reach the outlet by a transit time=length/speed. But it is not, the result depends on the time step used.

Please see the attached slides for details.

Problem with DPM.pptx

[Rob]

/forum/discussion/23093/why-ansys-employees-dont-download-attachmentsn

[lochihsiu]

Thank you, Rob. nPlease see the following figures. Thanks!nnnnUDF:nnn

[lochihsiu]

n

[Rob]

Is that with High Res tracking? The jump looks to be as particles enter/leave cells. What happens if you fix the particle step in the GUI? Simply, the trick to working out what's happening is to turn stuff off until it works, and then turn different things on until it breaks again. n

[lochihsiu]

Sorry, I am not sure what is High Res Tracking, I have attached my setup for DPM in the following figures, could you show me? nOther than the time step, I use default setup for the DPM. nIf I don't assigned a small time step, it works fine. But because our research is about turbulent dispersion, I need to use really small time step (dt~1E-6).nn n