Species Transport: Human Cough Virus Particles in the Coffee Shop

Human Cough Virus Particles in a Coffee Shop — ANSYS Fluent CFD Simulation

This project simulates the dispersion of virus-laden particles from a human cough within a coffee shop environment, using ANSYS Fluent.

Geometry and Mesh

The 3-D geometry was created in Design Modeler, representing the interior of a coffee shop as the computational domain. The model was meshed in ANSYS Meshing using an unstructured grid, with curvature-based refinement applied in regions requiring higher resolution. The total cell count is 4,578,388. Given the unsteady nature of the problem, a transient solver is used.

Methodology

The dispersion of virus particles is modeled using a two-way coupled Discrete Phase Model (DPM). Virus-carrying droplets are expelled from the patient's mouth through evaporating water droplets, injected at a temperature of 310 K, a velocity of 31.85 m/s, and a mass flow rate of 0.018 kg/s, over a time interval of 0 to 0.1 s.

Since droplet sizes vary during dispersion, the Rosin-Rammler logarithmic distribution is used to define the diameter range, with the minimum, maximum, and mean diameters used to determine the spread parameter and the number of diameter classes per injection. The species transport model is activated alongside the droplet model to capture this behavior.

For the discrete phase boundary conditions, particles passing through the patient's mouth boundary are set to "escape," meaning they leave the domain through this surface. Surfaces representing people, tables, and chairs use a "wall-film" condition, while the floor uses a "trap" condition, causing particles to accumulate on these surfaces upon contact.

The simulation runs as a transient case over a duration of 3 s, with a time step of 0.01 s. Turbulence is modeled using the RNG k-epsilon model, and the energy equation is enabled to resolve the temperature field within the domain.

Results

At the end of the simulation, particle tracking based on residence time is obtained for the final time step. An animation of the virus particle dispersion was also exported, illustrating how the particles spread throughout the coffee shop and gradually disappear over time.