Random Injector

A random injector injects particles into a region with a random point distribution. This injector is suitable if you wish to inject particles in a non-uniform, arbitrary manner.

When you create a random injector, you can assign parts from the Parts node under the Geometry node, as well as from the Regions node. However, the only parts available from the Parts node are the parts that you create from the New Shape Part menu: block, cone, cylinder, and sphere. If you choose geometry parts, you can optionally set the Region property of each part to match the region that contains the injector. This is useful if the part overlaps regions and you want to restrict the injection to a specific region.

To speed up the injection process, assign non-zero initial velocities. Particles with actual velocities pack faster and make room for new particles to be injected.

The Particle Packing Specification controls the number of injected particles, using the Porosity Limit, Particle Count, or Maximum Packing method. Porosity Limit is the default.

• If the Porosity Limit method is chosen, the injector works as follows:
  1. Check if the Injection cycle limit has been reached. If not, continue; otherwise stop.
  2. Randomly inject a number of particles. The Number of Seeds property sets this quantity.
  3. Eliminate any overlapping particles.
  4. Calculate the quantity of particles per unit volume -- also known as the porosity.
  5. If the calculated porosity is less than the Porosity Limit, repeat steps 1–4. Simcenter STAR-CCM+ continues injecting particles until the Porosity Limit is reached. The porosity limit for a fully packed volume is about 0.6.
• If the Particle Count method is chosen, the injector injects the specified number of non-overlapping particles, up to the limits of the volume.
• If the Maximum Packing method is chosen, the injector works as follows:
  1. The injector injects a specified number of particle seeds of small starting volume.
  2. In the first time-step, spherical particles grow from the seeds until there is no room that is left for growth.

  Maximum Packing sets the Initial Porosity Limit value to 0.3. This value works for most cases. Do not change it except in special cases. If there is a diverged packing or an undesired packing configuration, decrease this value to reduce the scale-up factors.

  For Maximum Packing, observe the following requirements:

  • The particles must be Spherical or Coarse Grain.
  • Assign a single region to the injector Inputs, not a geometry part.
  • Only one injector in a region can use the Maximum Packing method. You can have multiple random injectors in a region, but only one can use the Maximum Packing method.
  • The boundary mode for the injector region walls must be set to DEM mode. See Setting Phase Boundary Conditions, Mode.

User-specified settings for contact models are not taken into account during injection. They are saved before injection, then replaced by model values, and finally restored after the particles are generated.

In the example below, the injector injects particles into the cylindrical region, which is connected to the main volume using internal interfaces.