Intermittent particle distribution in synthetic free-surface turbulent flows

Tracer particles on the surface of a turbulent flow have a very intermittent distribution. This preferential concentration effect is studied in a two-dimensional synthetic compressible flow, both in the inertial (self-similar) and in the dissipative (smooth) range of scales, as a function of the compressibility C. The second moment of the concentration coarse grained over a scale r, < n(r)(2)>, behaves as a power law in both the inertial and the dissipative ranges of scale, with two different exponents. The shapes of the probability distribution functions of the coarse-grained density n(r) vary as a function of scale r and of compressibility C through the combination C/r(kappa) (kappa similar or equal to 0.5), corresponding to the compressibility, coarse grained over a domain of scale r, averaged over Lagrangian trajectories.