DPM: Beginner CFD Training Package — Ep 09
COVID-19 Transmission: Talking
- Lesson
- 09
- Run Time
- 15m 17s
- Published
- Aug 13, 2026
- Category
- DPM
- Course Progress
- 0%
Description
Airborne droplet transmission during speech is a key application of the Discrete Phase Model within Fluent, where dispersed particles must be tracked as a distinct phase moving through a continuous air field. This CFD study uses ANSYS Fluent to simulate coronavirus-laden droplets released during speech at sub-social-distance separations, modeling exhaled particles from an infected speaker and their transport toward another person within a defined indoor volume, in order to assess transmission risk while talking.
Methodology
The three-dimensional domain, measuring 1.6 m × 2 m × 2.6 m, is built in DesignModeler with two individuals facing each other 0.8 m apart, with the infected person's mouth defined as the particle source. The domain is discretized in ANSYS Meshing into 724,076 elements, and a transient solver is used to capture the time-evolving dispersion. The Discrete Phase Model is applied with unsteady particle tracking at a 0.001 s time step, treating exhaled droplets as a dispersed phase within the continuous air field. An injection is defined at the mouth surface using inert particles of 1×10⁻⁶ m diameter at 310 K, released over a 0 to 20 s window, with a custom profile prescribing particle velocity and mass flow rate: a sinusoidal velocity history peaking at 0.33 m/s, with mass flow rate scaled proportionally to that velocity. Turbulence is modeled using RNG k–ε, and the energy equation is solved to capture temperature effects on the flow.
Results Analysis
Post-processing provides particle tracks at multiple time instances, reported in terms of residence time and instantaneous velocity. Results show particle emission occurring during the initial 20 s, after which only previously emitted particles continue moving within the gap between the two individuals. The simulation indicates that speaking for 20 s without a mask can result in particles reaching the other person by approximately 40 s, illustrating a potential exposure pathway relevant to airborne transmission risk assessment.