COVID-19 Cough Model: Is 6 feet a safe social distance?


The COVID-19 pandemic has created a new “normal” for everyday life. Personal hygiene is one of the recommendations we are constantly being reminded of. Six feet is the recommended minimum distance between each person, but is it enough?

Utilizing Computational Fluid Dynamics (CFD), we can model the effectiveness of this 6 feet rule. The geometry for our simulation is from a CT scan of a volunteer human and is a very accurate representation of the mouth, trachea and lung system. Boundary conditions for this simulation are based on published scientific data of cough air velocity and volume as well as droplet sizes and distributions. Simulation starts with the fluid particles in the mouth and bronchial tree and a velocity that is a function of the geometry and flow rate. As the air and fluid droplets exit the mouth, they travel in the still air nearly 6 feet within 20 seconds. In those 20 seconds, the fluid disperses and breaks-up into smaller individual particles that eventually will drop to the ground.  However, some of the particles remain in a cloud-like area suspended in the air that could be inhaled by another person. The still air in our simulation also illustrates how ventilation patterns and filtration systems are important for removing these droplets in closed spaces, or how being outdoors with an ambient breeze could mitigate risks of transmission. If our subject had been wearing a mask, the cough velocity would be attenuated and the droplets would have been filtered and redirected… maybe something for a future simulation.

CFD is known to be used as a “virtual wind tunnel” for both the aircraft and automotive industries, but this simulation technology can be applied to other industries such as the medical field, building ventilation and HVAC. Many problems where gases, fluids, or air flow plays an important role are easily modeled in CFD. From predicting drug delivery to optimizing cardiovascular devices to predicting air flow patterns in a room, CFD can help gain insight and understanding through qualitative and quantitative analysis.

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