A churning cauldron of turbulence burns energy in two distinct ways. Vortices, like funnels in a whirlpool, swirl the fluid and rub layers against each other. Shock waves, like a sudden clap, sharply compress the gas and turn motion into heat. For a long time, it was thought that at very low viscosity, the rate of these losses stops depending on it. But what happens when the flow moves faster than sound and compression becomes the main effect? It turns out that energy losses proceed differently.

Numerical simulations showed that if the flow is slower than sound, energy losses approach one constant value. If the flow is much faster than sound, losses approach another constant. It is like two roads to the same finish line: one winding, one straight. The reason is that at high speeds, shock waves become dominant rather than vortices.

Previously, it was unclear whether this independence from viscosity persists in compressible turbulence and how it depends on flow speed. Now it is clear: the independence exists, but it is not a single one. For slow flows, it is one; for fast flows, another. This result could help build turbulence models for astrophysics and engineering calculations of supersonic flows.