How do you consider the effect of Brownian motion in Fluent software?
For submicron particles in laminar flow, you may want to include the effects of Brownian motion on the particle trajectories. To do so, enable the “Brownian Motion” option under the "Physical Models” tab. To include Brownian motion effects, you must also select the Stokes-Cunningham drag law in the "Drag Law” drop-down list under "Drag Parameters” and specify the Cunningham Correction.
Please refer to the attached document below for more information.