23.3.9 Point Properties for Air-Blast/Air-Assist Atomizer Injections

For an air-blast/air-assist atomizer, you will specify some of the same properties as for a plain-orifice atomizer. In addition to the position, axis (if 3D), temperature, mass flow rate, duration of injection (if unsteady), injector inner diameter, and azimuthal angles (if relevant) described in Section  23.3.7, you will need to specify the following parameters under Point Properties:

• outer diameter

  Set the outer diameter of the injector in the Injector Outer Diameter field. This value is used in conjunction with the Injector Inner Diameter to set the thickness of the liquid sheet ( $t$ in this equation in the separate Theory Guide).

• spray angle

  Set the initial trajectory of the film as it leaves the end of the orifice in the Spray Half Angle field ( $\theta$ in this equation in the separate Theory Guide).

• relative velocity

  Set the maximum relative velocity that is produced by the sheet and air in the Relative Velocity field.

• sheet breakup

  Set the value of the empirical constant that determines the length of the ligaments that are formed after sheet breakup in the Sheet Constant field ( $\ln (\frac{\eta_b}{\eta_0})$ in this equation in the separate Theory Guide).

• ligament diameter

  For short waves, set the proportionality constant ( $C_L$ in this equation in the separate Theory Guide) that linearly relates the ligament diameter, $d_L$, to the wavelength that breaks up the sheet in the Ligament Constant field.

• dispersion angle

  For a smooth distribution of the droplets, the initial velocities is varied within this dispersion angle. A scetch of the Atomizer Dispersion Angle for a flat fan atomizer is depicted in Figure  23.3.5.

See this section in the separate Theory Guide for details about how these inputs are used.