Simcenter STAR-CCM+ Secondary break up model in the lagrangian multiphase model

Due to the characteristic of the physical environment or process we are trying to simulate we may need to represent the situation that droplets in a liquid phase sometimes break up due to inhomogeneous surface forces.

STAR CCM+ provides four different breakup models and one user-defined breakup model to represent different types of droplet breakup phenomena.

In this article, we present how each of the four common break up models, except the user-defined break up model, is expressed through simulation calculations for reference.

Below is a picture of a representative type of droplet break up from the user-guide, and the response of a droplet to an inhomogeneous surface force is the deformation of the droplet, which is affected by the surface tension and viscous force of the droplet and is quantified by the Weber and Ohnesorge numbers. These two equations are also shown below.

This is the characteristic of each breakup model in the simulation model with the LMP injection speed set to 50m/s, and since the droplet diameter and speed may vary depending on the setting of variables in each model, this model applies the same number of child parcels in the default environment. Therefore, this article is not a quantitative comparison of each model, but rather a visualization of the breakup form and concept, so relative comparisons can be made.

1. KHRT Break up

This model was developed to replace the TAB Break up model and is the preferred model for high Weber numbers. The breakup form is a form in which small droplets are split around the center main droplet, and the main droplet becomes smaller and smaller in diameter as it moves forward.

2. Reitz-Diwakar Break up

This model is used to represent the Bag break up and Stripping break up models. The number of droplets increases as they break up into smaller droplets as they move forward.

3. SSD Break up

This model is intended to represent a catastrophic break up model, where a random break up occurs near the injection nozzle tip.

4. TAB Break up

This is a model for representing break up caused by vibration, where the main droplet rapidly progresses near the injection nozzle into multiple broken smaller droplets and is the preferred model at low Weber numbers.