  Turbulent motions in a fluid relax at a certain rate once stirring has
stopped. The role of the most basic parameter in fluid mechanics, the Reynolds
number, in setting the relaxation rate is not generally known. This paper
concerns the high-Reynolds-number limit of the process. In a classical
grid-turbulence wind-tunnel experiment that both reached higher Reynolds
numbers than ever before and covered a wide range of them ($10^4 < Re = UM/\nu
< 5\times10^6$), we measured the relaxation rate with the unprecedented
precision of about 2\%. Here $U$ is the mean speed of the flow, $M$ the forcing
scale, and $\nu$ the kinematic viscosity of the fluid. We observed that the
relaxation rate was Reynolds-number independent, which contradicts some models
and supports others.
