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.
Three impinging jets of silicone oil rebound without coalescence due to thin-film lubrication between the jets. The motion of the oil replenishes the thin layer of air separating the streams. The same phenomenon keeps droplets from coalescing as well. (Photo credit: BIF Lab, Department of Engineering Science and Mechanics, Virginia Tech) #