Thread by @JoshuaCAgar

Comparison of the wind flow of a person wearing a face shield (top panels) and a person not wearing face shields (bottom panels). [Tested a bit of stream tracing to determine the motion of particles]

Evidently, the particles traced experienced massive loss of momentum due to face shields (from red to blue). The loss of momentum led to increase in concentration. Also noted were the persistence of eddies (unsteady vortices).

[Velocity Field].

Note that airborne particles tend to go from regions of high flow energy to regions were less flow energy. The low-energy region initially is situated at the back of the head. Introducing the face shield situates the said region near the face.

The simulation was guided by the scientific laws that were taught to us in our primary and secondary education: The Law of Conservation of Mass and Newton's Laws of Motion.

The Conservation of Mass leads in the mathematical description of how particles, sediments, or any passive scalar is transported on a given flow called the Transport Equation.

The Conservation of Mass also leads mathematically to the Continuity Equation. Newton's 2nd Law of Motion leads to the Navier-Stokes Equations. These equations were numerically solved in the simulations using Computational Fluid Dynamics.

The good thing about scientific laws is that it manifest in natural processes that we normally encounter...

...like how the river sediments are deposited on the still portion of the river bank in a river bend, how we observe that dusts are deposited more at the back of vehicles than the front, ...

how flies anticipate an incoming swatting attempt due to the burst of positive pressure that they detect, how plastic pollution sadly deposited on our once-beautiful beaches.

That's why they are scientific laws in the first place: They survived the tests of time.