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22.16.1 Displaying of Trajectories

When you have defined discrete phase particle injections, as described in Section  22.12, you can display the trajectories of these discrete particles using the Particle Tracks panel (Figure  22.16.1).

Display $\rightarrow$ Particle Tracks...

Figure 22.16.1: The Particle Tracks Panel

The procedure for drawing trajectories for particle injections is as follows:

1.   Select the particle injection(s) you wish to track in the Release From Injections list. (You can choose to track a specific particle, instead, as described below.)

2.   Set the length scale and the maximum number of steps in the Discrete Phase Model panel, as described in Section  22.11.7.

Define $\rightarrow$ Models $\rightarrow$ Discrete Phase...

If stochastic and/or cloud tracking is desired, set the related parameters in the Set Injection Properties panel, as described in Section  22.12.5.

3.   Set any of the display options described below.

4.   Click on the Display button to draw the trajectories or click on the Pulse button to animate the particle positions. The Pulse button will become the Stop ! button during the animation, and you must click on Stop ! to stop the pulsing.


For unsteady particle tracking simulations, clicking on Display will show only the current location of the particles. Typically, you should select point in the Style drop-down list when displaying transient particle locations since individual positions will be displayed. The Pulse button option is not available for unsteady tracking.

Specifying Individual Particles for Display

It is also possible to display the trajectory for an individual particle stream instead of for all the streams in a given injection. To do so, you will first need to determine which particle is of interest. Use the Injections panel to list the particle streams in the desired injection, as described in Section  22.12.3.

Define $\rightarrow$ Injections...

Note the ID numbers listed in the first column of the listing printed in the FLUENT console. Then perform the following steps after step 1 above:

1.   Enable the Track Single Particle Stream option in the Particle Tracks panel.

2.   In the Stream ID field, specify the ID number of the particle stream for which you want to plot the trajectory.

Options for Particle Trajectory Plots

The options mentioned above include the following: you can include the grid in the trajectory display, control the style of the trajectories (including the twisting of ribbon-style trajectories), color them by different scalar fields and control the color scale, and coarsen trajectory plots. You can also choose node or cell values for display. If you are "pulsing'' the trajectories, you can control the pulse mode. Finally, you can generate an XY plot of the particle trajectory data (e.g., residence time) as a function of time or path length and save this XY plot data to a file.

Plotting particle trajectories can be very time consuming, therefore, to reduce the plotting time, a coarsening factor can be used to reduce the number of points that are plotted. Providing a coarsening factor of $n$, will result in each $n$th point being plotted for a given trajectory in any cell. This coarsening factor is specified in the Particle Tracks panel, in the Coarsen field and is only valid for steady state cases. For example, if the coarsening factor is set to 2, then FLUENT will plot alternate points.


Note that if any particle or pathline enters a new cell, this point will always be plotted.

To reduce plotting time in transient cases, FLUENT has available an option to skip plotting every $n^{\rm th}$ particle in an injection. Selecting this option is also done in the Particle Tracks panel menu by specifying a nonzero integer in the Skip field. For example, if an individual stream is selected and the skip option is set to 1, every other particle will be plotted. If the entire injection is selected with a skip option of 1, every other particle will be plotted for all streams in the injection.

These options are controlled in exactly the same way that pathline-plotting options are controlled. See Section  28.1.4 for details about setting the trajectory plotting options mentioned above.

Note that in addition to coloring the trajectories by continuous phase variables, you can also color them according to the following discrete phase variables: particle time, particle velocity, particle diameter, particle density, particle mass, particle temperature, particle law number, particle time step, and particle Reynolds number. These variables are included in the Particle Variables... category of the Color By list. To display the minimum and maximum values in the domain, click the Update Min/Max button.

Graphical Display for Axisymmetric Geometries

For axisymmetric problems in which the particle has a nonzero circumferential velocity component, the trajectory of an individual particle is often a spiral about the centerline of rotation. FLUENT displays the $r$ and $x$ components of the trajectory (but not the $\theta$ component) projected in the axisymmetric plane.

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