Learning Forum

[Gerhard Holzinger]

I have a case with transient DPM (unsteady particle tracking using the fluid flow time step) which reports incomplete particle trajectories.

Interaction with the continuous phase is turned off, and the continuous flow fields are not solved for, hence I am using a frozen flow assumption based on a pre-computed flow.

The log reports: number tracked = some number, incomplete = another non-zero number

The warning message says: x% of the total discrete phase mass was not tracked for the expected residence time: s less on a massweighted average (which is y % of their total age or z % of the last time step).

 

How does Fluent decide whether a particle trajectory is incomplete?

[Rob]

Particles go "incomplete" when the number of update steps (set in DPM panel Max steps) is exceeded. This can be due to an excessive flight time, too big a time step or particles that are caught in a small region but change cells very frequently. How high a number are you losing? 

[Gerhard Holzinger]

It affects only individual particles.

With unsteady tracking, the default for max number of steps is 500.

Does this mean, that for each time step there's a maximum number of 500 integration steps for computing the particle trajectory?
And whenever a particle is reported as incomplete, then it has exceeded this maximum number?

[Rob]

Pretty much. You can increase the number of steps but it's also a trade off between cpu/time and the odd lost parcel.