Why it is necessary to wear the mask? FLOW-3D simulation comparison

Given the period of health emergency related to COVID-19 we wanted to clarify with this video why it is necessary to wear the mask correctly.

You can observe 3 CFD simulations made by FLOW-3D in which, respectively, the subject does not wear the mask, does not hold it close to the nose and finally wears it correctly.

As you can see only in case the mask is adherent to the face the airflow around the subject is greatly reduced. In other cases the air displaced by the breath moves significantly away from the subject, either frontally or laterally.

To better visualize the movement of the air, a tracer has been used to indicate the movement of the air and has no reference to real particles.

One last observation: looking carefully at the video, it is easy to understand why, wearing the mask, fogs the glasses so easily :-)