Measurement of entropy production rate in compressible turbulence

The rate of change of entropy $\dot S$ is measured for a system of particles floating on the surface of a fluid maintained in a turbulent steady state. The resulting coagulation of the floaters allows one to relate $\dot S$ to the the velocity divergence and to the Lyapunov exponents characterizing the behavior of this system. The quantities measured from experiments and simulations are found to agree well with the theoretical predictions.