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Schlieren imaging is a flow visualization method that takes advantage of changes in the density and index of refraction of a fluid. Light is projected through the medium and into a camera. However, before the light reaches the camera, some of the refracted light is blocked, usually by a knife edge.
Since the equipment (particularly the parabolic/spherical mirrors) needed for this is expensive, I borrowed some from Cal Poly's Mechanical Engineering Department. One constraint is that the size of the imaging field is related to the size (and cost) of the mirrors.
The setup I used is considered a "Z" formation (as opposed to the "V" setup that is also commonly used) due to the shape of the path that the light takes from the source to the camera. Most setups are monochrome since the knife edge (in this case, the edge of a piece of aluminum foil taped to a cardboard cutout) simply blocks refracted light and produces dark areas on the image. I experimented with replacing the knife edge with color filters, which produced some interesting and colorful results.
My schematic of the setup I created.
The actual setup in my garage.
Results
Results
I experimented with two subjects: a tea light candle and a can of compressed air. Blowing on the candle creates interesting projections due to the turbulent airflow. I had read online that the plastic straw nozzle on compressed air cans creates supersonic flow, so I was very excited to capture the resulting Mach diamonds. I also retouched the images below to remove circular shadows created by tiny defects in the mirrors.
I tried my hand at making a GIF from some of the frames as well:
For the last two images, I placed a small piece of sheet metal above the candle to see how the hot air rises around it. Looks cool!
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