23.3 Setting Initial Conditions for the Discrete Phase

The primary inputs that you must provide for the discrete phase calculations in ANSYS FLUENT are the initial conditions that define the starting positions, velocities, and other parameters for each particle stream and the physical effects acting on the particle streams, requiring additional particle properties. You will define the initial conditions for a particle/droplet stream by creating an "injection'' and assigning properties to it.

The required initial conditions depend on the injection type, while the physical effects are selected by chosing an appropriate particle type. For some injection types you can provide a particle size distribution, like the Rosin-Rammler distribution, see Section  23.3.13.

The initial conditions provide the starting values for all of the dependent discrete phase variables that describe the instantaneous conditions of an individual particle, and include the following:

• position ( $x$, $y$, $z$ coordinates) of the particle

• velocities ( $u$, $v$, $w$) of the particle

  Velocity magnitudes and spray cone angle can also be used (in 3D) to define the initial velocities (see Section  23.3.5). For moving reference frames, relative velocities should be specified.

• diameter of the particle, $d_p$

• temperature of the particle, $T_p$

• mass flow rate of the particle stream that will follow the trajectory of the individual particle/droplet, $\dot{m}_p$ (required only for coupled calculations)

• additional parameters if one of the atomizer models described in this section in the separate Theory Guide is used for the injection

  When an atomizer model is selected, you will not input initial diameter, velocity, and position quantities for the particles due to the complexities of sheet and ligament breakup. Instead of initial conditions, the quantities you will input for the atomizer models are global parameters.

These dependent variables (temperature, diameter, etc.) are updated according to the equations of motion ( this section in the separate Theory Guide) and according to the heat/mass transfer relations applied ( this section in the separate Theory Guide) as the particle/droplet moves along its trajectory. You can define any number of different sets of initial conditions for discrete phase particles/droplets provided that your computer has sufficient memory.