### 8.10.1. Particle Coupling Control

#### 8.10.1.1. First Iteration for Particle Calculation

This parameter sets the iteration number when particles are first tracked. A few iterations should be completed to let the continuous phase settle down from the initial guess before particles are introduced. If the convergence behavior is not steady by this iteration number, then you can increase the value of the First Iteration for Particle Calculation parameter above default, which is 10 in a steady-state simulation and 1 in a transient simulation.

When restarting a run, the iteration number refers to the total iteration number and not that of the current run.

This parameter applies to fully coupled particle phases and transient runs where the specified First Iteration for Particle Calculation refers to coefficient loop iterations.

#### 8.10.1.2. Iteration Frequency

Particles are injected during execution of the CFX-Solver at regular iteration intervals. The particles are then tracked using the fluid solution field from the previous iteration. Once the particle paths have been calculated, the particle sources to mass and momentum equations are calculated. The source terms are applied to the fluid equations at each subsequent iteration until they are recalculated at the next injection.

The Iteration Frequency parameter is the frequency at which particles are injected into the flow after the First Iteration for Particle Calculation iteration number. This introduces particle source terms that will often cause an immediate rise in the convergence residual levels. The iteration frequency allows the continuous phase to settle down between injections.

The default value for Iteration Frequency is `5` in a steady-state simulation and `1` in a transient simulation.

If the continuous phase reaches its convergence criterion before the particle calculation reaches its own convergence criterion, then the code automatically overrides the value specified for the iteration frequency, and starts to track the particles on every iteration.

The parameter applies to fully coupled particle phases and transient runs where the specified iteration interval refers to coefficient loop iterations.

#### 8.10.1.3. Particle Source Change Target

This parameter applies only to fully-coupled particle phases and is used to determine when the particle part of the calculation has converged, as follows:

The absolute value of the particle source for a given momentum equation is summed over all vertices; let this value be . When the inequality Equation 8–3 is satisfied for all momentum equations, the particle part of the calculation is deemed to have converged.

| (8–3)

The default value is 0.01 and it is unlikely that you will need to change this.

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