SSD Breakup Model Reference

In the Stochastic Secondary Droplet (SSD) breakup model, breakup is modeled as catastrophic, a random process unrelated to original droplet size. This results in a log normal distribution of droplet diameters in the long time limit.

The particles interact with the Eulerian fluid phase as they travel. Particles break up when three criteria are met:

• The particle radius is larger than the critical radius (calculated from local droplet conditions using Eqn. (3114)).
• The Weber number (calculated from local droplet conditions) is larger than a critical Weber number (set in the interface).
• The particle's local time (the accumulated residence time) is larger than the breakup time (Eqn. (3115)). The model tracks parcels as they cross the domain and compares the residence time with a locally evaluated breakup time. The residence time is only calculated accumulating on parcels with a radius larger than a critical radius and a Weber number larger than a critical Weber number.

When the particle breaks up, the local time is reset for the new parcels.

You can control the average number of particles per child parcel and the maximum number of child parcels formed in each breakup event using the Target Count and Maximum Child Parcels properties. The model uses these values when calculating the size, number of parcels, and particles per parcel (parcel count) of the child parcels. This gives you some control over the discretization of the spray.

Note that neither Target Count nor Maximum Child Parcels changes the physics of the breakup event, since these parameters do not change the diameter distribution functions. Rather, these parameters influence the total number of parcels in the calculation and thus the relative expense of the computation. A larger number of samples usually means an improved representation of the droplet size distribution.