23.3.6 Point Properties for Surface Injections

For surface injections, you will define all the properties described in Section  23.3.3 for single injections except for the initial position of the particle streams. The initial positions of the particles will be the location of the data points on the specified surface(s). Note that you will set the Total Flow Rate of all particles released from the surface (required for coupled calculations only). If you want, you can scale the individual mass flow rates of the particles by the ratio of the area of the face they are released from to the total area of the surface. To scale the mass flow rates, select the Scale Flow Rate By Face Area option under Point Properties. For the massless particle type, you will not need to enter any information to define a surface injection. The particle velocities are set by the solver equal to the velocities of the continuous phase at the injection points.

Note that many surfaces have nonuniform distributions of points. If you want to generate a uniform spatial distribution of particle streams released from a surface in 3D, you can create a bounded plane surface with a uniform distribution using the Plane Surface dialog box, as described in Section  28.6. In 2D, you can create a rake using the Line/Rake Surface dialog box, as described in Section  28.5.

In addition to the option of scaling the flow rate by the face area, the normal direction of a face can be used for the injection direction. To use the face normal direction for the injection direction, select the Inject Using Face Normal Direction option under Point Properties (Figure  23.3.10). Once this option is selected, you only need to specify the velocity magnitude of the injection, not the individual components of the velocity magnitude.

Note also that only surface injections from boundary surfaces will be moved with the mesh when a sliding mesh or a moving or deforming mesh is being used.

For moving or deforming mesh simulations only zonal surfaces can be selected.

A nonuniform size distribution can be used for surface injections, as described below.

Using the Rosin-Rammler Diameter Distribution Method

The Rosin-Rammler size distributions described in Section  23.3.13 for group injections is also available for surface injections. If you select one of the Rosin-Rammler distributions ( rosin-rammler or rosin-rammler-logarithmic), you will need to specify the following parameters under Point Properties, in addition to the initial velocity, temperature, and total flow rate:

• Min. Diameter

  This is the smallest diameter to be considered in the size distribution.

• Max. Diameter

  This is the largest diameter to be considered in the size distribution.

• Mean Diameter

  This is the size parameter, $\overline{d}$, in the Rosin-Rammler equation (Equation  23.3-3).

• Spread Parameter

  This is the exponential parameter, $n$, in Equation  23.3-3.

• Number of Diameters

  This is the number of diameters in each distribution (i.e., the number of different diameters in the stream injected from each face of the surface).

ANSYS FLUENT will inject streams of particles from each face on the surface, with diameters defined by the Rosin-Rammler distribution function. The total number of injection streams tracked for the surface injection will be equal to the number of diameters in each distribution ( Number of Diameters) multiplied by the number of faces on the surface.