SCHLIEREN IMAGE

While I was doing my research for my blog on “Are Super Sonic Commercial Flights Back?” I came across a very fascinating image that shows the shock waves around the X-59 aircraft. When I searched about it a little more, I came to know that it is known as Schlieren Image which is used to photograph the airflow around the object.

Image credit: NASA

To take a Schlieren Image you need a mirror, a light source, a knife edge, and a camera. What happens here is you shine a light from a light source which is then reflected from the mirror into our camera lens. The knife edge is placed in between the mirror and camera lens such that it cuts the light in half.

Image credit: ResearchGate.net

It works by detecting the change in the refractive index of air. The refractive index is the ratio of the Speed of light in a vacuum and the speed of light in any medium. For air, this ratio is approximately 1 (1.0003), but it varies with temperature changes.

Image credit: Veritasium [YouTube]

The difference in refractive index with respect to temperature is very difficult to notice with our eyes. But with the help of Schlieren Image/Schlieren Photography, we can detect these changes. Whenever there is a change in the refractive index of air, the light will bend and will create areas of light and shadow. These are captured by our camera and thus we can see the flow of air.

One important area where Schlieren Imaging found its application in in aerodynamics. It helps in studying the shockwave in supersonic and hypersonic flights.

You can find videos on YouTube where people are experimenting with Schlieren Image by taking images of different objects below: 

1. How To See Air Currents by Varitasium

2. Shockwave Shadows in Ultra Slow Motion (Bullet Schlieren) - Smarter Every Day 203 by SmarterEveryDay