Krypton Tagging Velocimetry

Imagine a super-fast airplane flying, five or six times the speed of sound. The air flowing over its skin is incredibly chaotic and turbulent, like a raging river. Back in the 1960s, a scientist named Morkovin proposed a clever idea: if you just account for how the air gets squeezed and stretched (its density changes), this super-fast, chaotic air actually behaves a lot like the slow-moving, well-understood flow of water in a pipe. This makes it much easier to predict things like friction and heat. The problem was, nobody could properly measure one of the key 'up-and-down' wobbles in this chaotic flow to prove it. This study used a special laser technique with krypton gas to finally measure that wobble. They found it matched Morkovin's old idea perfectly, confirming a foundational principle of high-speed flight.