Force a fluid gently and it responds in orderly fashion—points within the fluid trace out smooth, parallel streamlines at steady speeds in what is known as laminar flow. In fact, the response is so orderly that, absent significant diffusion, reversal of the forcing returns each point to its original location.
But disturb the fluid more vigorously so that the Reynolds number—the ratio of inertial to viscous forces—becomes large, and the well-organized flow gives way to the chaotic whirls and eddies of turbulence, with each point subject to abrupt and unpredictable changes in direction and speed. Both flow regimes are beholden to the same Navier–Stokes equations. But whereas laminar flow is easily understood and modeled, turbulent flow is among the most mysterious phenomena in fluid mechanics.
Now, two independent experiments—one by Detlef Lohse and colleagues at the University of Twente in the Netherlands,1 the other by Daniel Lathrop and Matthew...
