Decorrelating a compressible turbulent flow: an experiment

Floating particles that are initially distributed uniformly on the surface of a turbulent fluid, subsequently coagulate, until finally a steady state is reached. This being so, they manifestly form a compressible system. In this experiment, the information dimension D_1, and the Lyapunov exponents of the coagulated floaters, are measured. The trajectories and the velocity fields of the particles are captured in a sequence of rapidly acquired images. Then the velocity sequence is randomly shuffled in time to generate new trajectories. This analysis mimics the Kraichnan ensemble and yields properties of a velocity correlation function that is delta-correlated in time (but not in space). The measurements are compared with theoretical expectations and with simulations of Boffetta et al., that closely mimic the laboratory experiment reported here.