Schlieren Flow Visualization

Schlieren Flow Visualization

Schlieren Flow Visualization is an optical technique used to visualize small changes in the index of refraction in air.

Experimental Setup

Experimental Setup

A light source is focused onto a pinhole to create a high intensity point source. The point source is located two focal lengths from a 6" spherical mirror (f = 1.5 m) to produce an image of the same size on a razor blade. The razor blade is positioned to block half of the light reflected by the mirror, while the other half of the light is picked up by the camera. The camera lens is focused on the objects held in front of the mirror.

Objects held in front of the mirror will disrupt the air, changing the index of refraction, and thereby changing the amount of light which is blocked by the razor blade. Depending on whether the index of refraction of the air is increased or decreased, more or less light will be blocked by the razor blade, and therefore more or less light will be picked up by the camera. This produces an image where small changes in refractive index can easily be seen, allowing heat and gases invisible to the human eye to be easily seen.

Experimental Results

Many different objects were observed to produce changes in refractive index, including the heat rising from a hand and a person exhaling. But the most striking results were produced from a butane torch, both before and after being ignited, and a can of compressed air. Images of these can be seen below.

Change in optical density produced by butane (left) and ignited butane (right)

Change in refractive index produced by compressed air