In educational wind tunnels fog can be used to recognise air flow patterns / aerodynamic properties of different objects. The Concept Aerotech Smoke Wand creates a single and precise point source of fog for this very purpose.
A rake of fog is also a very effective way of understanding the overall airflow pattern of an object. A variant of the ViCount fog machine can be used for this. The ViCount can be configured to use both water based fog fluid and oil based fluids.