Mach diamonds in the garage!
So this isn't an F-16 style afterburner, but rather a shadowgraph of air coming out of my air compressor (through the blow gun) made with nothing more than a single white LED as a point light source and my phone (and a wall, where the shadows are cast) There's a way more fancy and sensitive way to get these kinds of visualizations, called Schlieren photography which involves parabolic mirrors and a knife edge, but unfortunately my personal parabolic mirror happens to be in a telescope 3000+ miles away, so we'll have to just settle on Ikea lights and tape for the moment.
You can clearly see the standing waves as the air comes out. The pressure is only about 85 PSI, but you can see the shape and spacing change as I vary the flow. This sort of valve is not great at fine control, but you get the idea.
Mach diamonds, or shock diamonds are "a formation of standing wave patterns that appear in the supersonic exhaust plume" - thank you Wikipedia.
I'm mostly impressed that my air compressor goes supersonic .
