flowviz:

Lasers and impacting droplets can’t fail to impress. PIV is a flow viz technique in which small ‘seeder’ particles are released into a flow and laser light and cameras are used to map the positions of these particles. From these measurements flow quantities like velocity can be calculated.

In this example the interplay between a liquid surface and the air around it is seen as a drop collides with the liquid surface. It looks like the seeding machine is just off the left of screen and producing some pretty good vortices.

Source: IntellectualVentures