Understanding virus dispersion in rooms has become more important for public health and safety, especially regarding the transmission of respiratory diseases via coughing and sneezing incidents. When an infected individual coughs or sneezes, droplets carrying the virus are released into the air, forming dispersion. These droplets experience substantial modifications, including breakup events, wherein larger droplets break into smaller aerosol particles capable of remaining airborne for long times. Employing ANSYS Fluent’s Discrete Phase Model (DPM), researchers can monitor the route and behavior of virus-laden particles in constrained environments, including essential parameters such as droplet dispersion evaporation, and particle-air interactions. This is our ultimate goal of the current CFD study, which is established based on several reference papers:

• Reference [1]: Pendar, Mohammad-Reza, and José Carlos Páscoa. “Numerical modeling of the distribution of virus carrying saliva droplets during sneeze and cough.” Physics of Fluids8 (2020).
• Reference [2]: Fontes, D., et al. “A study of fluid dynamics and human physiology factors driving droplet dispersion from a human sneeze.” Physics of Fluids11 (2020).
• Reference [3]: Issakhov, Alibek, et al. “A numerical assessment of social distancing of preventing airborne transmission of COVID-19 during different breathing and coughing processes.” Scientific Reports1 (2021): 9412.

Figure 1: Virus transmission risk in 2-meter in-person appointment inside a room [1]

Simulation Process

Two people are inside a closed room, standing in 1.3m distance from each other. The domain is modeled via Spaceclaim software and discretized into 412131 polyhedra cells using Fluent Meshing. One of them is infected and cough. So that the droplets carrying the virus is spread all over. This process requires usage of Discrete Phase Model (DPM), Species transport and several sub-models that helps in modeling primary and secondary breakup. The sub-models are Stochastic collisions, Coalescence and Breakup. In addition, unsteady-unsteady approach governing the simulation of the multiphase problem (1 continuous + 1 discrete phase). In balance, a high computational cost is expected regarding breakup model and droplets evaporation.

Figure 2: Geometry model of Virus Distribution by Coughing Considering Breakup DPM CFD Simulation

Post-processing

The particle diameter distribution exhibits distinct stratification, with larger droplets (2.33e-4 to 3.33e-4 m) rapidly dropping under gravitational influence, when smaller particles (3.3e-5 to 9.9e-5 m) remain suspended and traverse greater horizontal distances. The breakup phenomena occur particularly strongly in the center plume region, where bigger droplets fragment, resulting in a cloud of smaller aerosol particles with improved dispersion properties. The particle velocity magnitudes vary from 0 to 5.02 m/s, with peak velocities recorded soon post-expulsion, followed by rapid deceleration due to interactions with the ambient air.

Figure 3: Particle diameter distribution in Virus Distribution by Coughing Considering Breakup DPM CFD Simulation

Figure 4:: Velocity Magnitude in Virus Distribution by Coughing Considering Breakup DPM CFD Simulation

The residence time study reveals that this severe coughing incident, lasting within a few seconds (up to 0.74 seconds), generates an unusual dispersion pattern that greatly affects the surrounding area. The contours demonstrate that particles with extended residence durations (depicted in red) are associated with smaller diameter particles, which remain suspended in the air and present a heightened transmission risk. The simulation depicts the critical initial phases of virus propagation, wherein the interaction of particle breakup and air dynamics generates an extensive dispersion pattern, notably visible in the lateral expansion of the particle cloud. This behavior is indicative of respiratory episodes that may facilitate airborne transmission in enclosed spaces.