Decay of Turbulence at High Reynolds Numbers

Turbulent motions in a fluid decay at a certain rate once stirring has stopped. The role of the most basic parameter in fluid mechanics, the Reynolds number, in setting the decay rate is not generally known. This Letter concerns the high-Reynolds-number limit of the process. In a classical grid-turbulence wind-tunnel experiment that both reaches higher Reynolds numbers than ever before and covers a wide range of them (10^{4}<Re=UM/ν<5×10^{6}), we measure the decay rate with the unprecedented precision of about 2%. Here U is the mean speed of the flow, M is the forcing scale, and ν is the kinematic viscosity of the fluid. We observe that the decay rate is Reynolds-number independent, which contradicts some models and supports others.