Difference Between Particle Parcel and Stream — Lesson 1

What is the difference between particles, parcels, and streams?

In unsteady discrete phase modelling (DPM): It is very expensive to track each individual particle in a particle flow system. Instead of tracking each particle, Fluent software tracks parcels. Parcels contain particles with the same properties, including diameter, velocity, and position. The behavior of each parcel is determined by the behavior of the particles inside.

The number of particles in a parcel can be obtained using macro p->number_in_parcel. The number of particles in each parcel can be a fractional number.

Streams are defined for injecting the parcels in the computational domain. ‘N’ streams means ‘N’ locations of parcel injection. The stream mass flow rate and number of particles in a parcel are related as:

Number of particles in a parcel = (Stream mass flow rate*Injection time interval)/ (Mass of single particle)

The number of particle streams that you specify is the number of parcels that get injected after each injection time interval.

In steady DPM: The number of particles in a parcel is not valid for steady tracking. Instead, there is "strength," which is essentially the number of particles in a parcel/second and is calculated as:

Strength = (Stream mass flow rate)/(Mass of single particle)

Clarification: Ansys Fluent user documentation refers to parcels as "particles."