High Speed Schlieren Photography
The primary objective of Schlieren photography is to make transparent mediums such as gases and liquids visible. Once the currents in these mediums are visible, investigation or study of their properties and behavior becomes much easier.
Schlieren photography allows visualization of density gradients due to changes in refractive index. Light rays are bent as one transparent medium passes to another one of different density. For example, as one gas passes to another or among currents of the same gasses at different temperatures (i.e. heated air), it is possible to see light rays that are bent around the current movement.
The study of these density gradients photographically can be invaluable in critical design work. Burning fuels in combustion engineering, heat transfer studies, ballistics and aeronautical design are just a few examples of areas that benefit from the use of Schlieran methodologies.
The photograph shown demonstrates a simple Schlieren image of a burning candle with heat and gasses visible rising in a column from the top of the flame. The small object to the left was a pellet that was fired (right to left) through the gasses. The wavy lines to the right of the pellet were density gradients formed behind the pellet by its rapid movement through the gasses.
The movement of the pellet was stopped by using a high speed flash, but the gasses and resulting trail through them was recorded by the Schlieren technique. For more information about this type of photography, please continue browsing the "Technical Photography" section of my web site.