Learning Forum

[lydau]

Hi all,
I am working on droplet transmission from human exhalation in a room using Lagrangian Particle Tracking (LPT) with evaporation model. Both steady state and transient simulations ran well without error. However, I'm having issues extracting the particle variables (diameter, number rate, temperature, velocity, components' mass fraction, etc) at any point (spatially) within the room. From CFX documentation, particle variables in LPT can be track variables or field variables and that spatial values of particle information are captured with particle field variables. Unfortunately, I've been unable to get these variables for any points in the domain. I am wondering if anyone have worked on LPT in CFX and how the particle field variables are extracted.
Thanks in anticipation of your feedback.

[rfblumen]

For Particle Transport Modeling in CFX, two types of variables are available: Particle Track Variables and Particle Field Variables. The particle variables that you mention (diameter, number rate, temperature, velocity, components' mass fraction, etc.) are associated with Particle Track Variables and by default are only available for quantitative post-processing if the particle tracks (and the associated track variables) are exported from Post and post-processed outside of CFD-Post. This can be done using Fortran or similar where for a given (x,y,z) location, each particle track is followed from start to end and the minimum distance (along with the particle track variables) to the desired point is determined. The particle track variable values for each particle track can then be tabulated and some averaging of the information can be done for tracks that are within some radius of the desired point.
Another approach, if the goal is post-processing Particle Track Variables within CFD-Post at a specific (x,y,z) location, is to work with Particle Vertex Variables (see 16.3.2.3. Particle Vertex Variables in the CFX Reference Guide). In CFX-Pre, variables such as Average Mean Particle Diameter, Averaged Particle Number Rate, etc. can be selected from the Extra Output Variables List in the Output Control section. In CFD-Post, these variables can be post-processed in the same way as fluid variables. A point can be created in the domain at some (x,y,z) and the probe function can be used in the Function Calculator to extract the desired particle variables.