### 17.3.6. Particle Tracking Parameters

`pt distribute trans particles`
Type | Logical
Default Value | t
Description | Uniformly distribute transient particles over the time step in a transient run. If this parameter is set to `'f'`, all particles are injected at the start of the time step.
`pt extrap vel for integ`
Type | Logical
Default Value | f
Description | Use extrapolation of the particle velocity during particle integration. This may be helpful for cases with streamline curvature.
`pt fluid var interpolation option`
Type | Integer
Default Value | 1 (for cases that involve particle reactions) 2 (for cases that do not involve particle reactions)

Description

This parameter controls whether fluid variables are interpolated to the current particle position.

Values:

0 = No interpolation. All fluid variables are assumed to be constant within a control volume.

1 = Interpolate all fluid variables except those that represent species concentrations.

2 = Interpolate all fluid variables.

`pt force export massflow`
Type | Logical
Default Value | f
Description | When this parameter is set to `'t'`, particle mass flows are always written to the results files. Otherwise they will only be written if they are used in CEL expressions or monitors.
`pt linear src coef multiplier`
Type | Real
Default Value | 1.0
Description | Defines a factor which multiplies the linearization coefficient of the particle sources.
`pt maximum particle temperature`
Type | Real
Default Value | 3000.0
Description | Defines upper bound for the particle temperature in units of Kelvin [K].
`pt minimum diameter`
Type | Real
Default Value | 1.E-8
Description | Defines the minimum allowed particle diameter. Tracking of a particles is stopped if its diameter falls below this value.
`pt minimum eddy life time`
Type | Real
Default Value | 0.0
Description | Defines the minimum eddy life time for turbulent dispersion of particles.
`pt time interpolation`
Type | Integer
Default Value | 1
Description | Used in a transient run in order to decide how fluid quantities have to be interpolated to the current particle time. Possible values are: 0 = Use newest time level 1 = Linear interpolation between current and previous time levels 2 = Quadratic interpolation between current and two previous time levels
`pt tracks in absolute frame`
Type | Logical
Default Value | f
Description | Output tracks in absolute frame of reference. Important for postprocessing of non-transient RFR cases. Not required for transient cases.
`pt zone specific tracks`
Type | Logical
Default Value | t

Description

This parameter controls the way how particle tracking information is written out to the results file. By default, this expert parameter is set to `'t'` and particle tracks will contain domain information. This information enables CFD-Post, for example, to display particle tracks on a user specified domain only.

In a multi-configuration run, where the number of domains may vary across simulations, it can happen that the interpolator can no longer map the source domain to a target domain. In this case, the source particle tracks are not copied to the target domain and are therefore lost. To avoid this problem, it is suggested that you set the `pt zone specific tracks` parameter to `'f'` for multi-configuration runs. This enables the interpolator to always copy particle tracks to the target file, regardless of any changes in the number of source to target domains.

Note: When the pt zone specific tracks parameter is set to `'f'`, no domain filtering will be possible in CFD-Post.

`solve particles`
Type | Logical
Default Value | t
Description | Flag for controlling whether or not the controller solves the particle transport equations

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