BYU Mechanical Engineering professor Tadd Truscott studies fluid flow and the visualization and analysis of fluid phenomena. In other words, he takes pictures of splashes.
One of his images was selected as the winning entry in the 2009 American Physical Society Division of Fluid Dynamics (APSDFD) Gallery of Fluid Motion. Physics of Fluids published the photo in their September 2010 issue, and now Cosmos magazine has published a compilation of those winners.
The images are created by setting up an slr camera with a large lens (100 mm) with a narrow depth of field F-2.8 and focusing on the center of the droplets. The lighting is done by several halogen bulbs as back lighting, with a narrow black paper in front of the lights only where the lens is. The index of refraction of the oil is such that it can bend the light differently from the alcohol around it, which causes the light spots seen in the image creating the effect seen here.
The spreading droplet is heavier than the surrounding fluid causing it to descend and spread outward. The fingering is a natural result of having a denser fluid on top of a lighter one. “These images are particularly interesting,” commented Truscott. “People may not think of them as just a droplet of oil in alcohol, but instead see other interesting forms.”
Click here to see Cosmos’ photo compilation: