Schlieren photography

Common card · No. 269782

Schlieren photography is a process for photographing optical inhomogeneities in transparent media that are not necessarily visible to the human eye, typically used to study fluid flow, like the flow of air around objects in aeronautical engineering. The conventional schlieren imaging system was developed in 1864 by the German physicist August Toepler to detect schlieren (striae, streaks) in optical glass. The process works by imaging the deflections of light rays that are refracted by a moving fluid, allowing normally unobservable changes in a fluid's refractive index to be seen. Because changes to flow rate directly affect the refractive index of a fluid, one can therefore photograph a fluid's flow rate (as well as other changes to density, temperature, and pressure) by viewing changes to its refractive index. Using the schlieren photography process, other unobservable fluid changes can also be seen, such as convection currents, and the standing waves used in acoustic levitation.

Read on Wikipedia · Image NASA, Public domain