I chose this image of an RS-88 liquid rocket engine hot fire because it captures both the beauty and physics of supersonic flow. I especially like the structure of the mach diamonds and color variation within the exhaust plume, where the supersonic flow expands from the nozzle and adjusts toward the surrounding atmospheric pressure through shock and expansions. And artistically the bright blue and orange plume against the complex test stand hardware makes the flow itself the most visually striking part of the image.

Attribution: NASA/MSFC/Emmett Given, 2003

Source: https://www.nasa.gov/image-article/rocket-engine-hardware-testing-historic-nasa-marshall-center-test-stands/