Lyapunov exponents of heavy particles and tracers advected by homogeneous and isotropic turbulent flows are investigated by means of direct numerical simulations. For large values of the Stokes number, the main effect of inertia is to reduce the chaoticity with respect to fluid tracers. Conversely, for small inertia, a counterintuitive increase of the first Lyapunov exponent is observed. The flow intermittency is found to induce a Reynolds number dependency for the statistics of the finite-time Lyapunov exponents of tracers. Such intermittency effects are found to persist at increasing inertia. (c) 2006 American Institute of Physics.

We present the results of direct numerical simulations of heavy particle transport in homogeneous, isotropic, fully developed turbulence, up to resolution 512(3) (R-lambda approximate to 185). Following the trajectories of up to 120 million particles with Stokes numbers, St, in the range from 0.16 to 3.5 we are able to characterize in full detail the statistics of particle acceleration. We show that: (i) the root-mean-squared acceleration arms sharply falls off from the fluid tracer value at quite small Stokes numbers; (ii) at a given St the normalized acceleration a(rms)/(is an element of(3)/nu)(1/4) increases with R-lambda consistently with the trend observed for fluid tracers; (iii) the tails of the probability density function of the normalized acceleration a/a(rms) decrease with St. Two concurrent mechanisms lead to the above results: preferential concentration of particles, very effective at small St. and filtering induced by the particle response time, that takes over at larger St.

We present the results of direct numerical simulations (DNS) of turbulent flows seeded with millions of passive inertial particles. The maximum Reynolds number is Re-lambda similar to 200. We consider particles much heavier than the carrier flow in the limit when the Stokes drag force dominates their dynamical evolution. We discuss both the transient and the stationary regimes. In the transient regime, we study the growth of inhomogeneities in the particle spatial distribution driven by the preferential concentration out of intense vortex filaments. In the stationary regime, we study the acceleration fluctuations as a function of the Stokes number in the range St is an element of [0.16 : 3.3]. We also compare our results with those of pure fluid tracers ( St = 0) and we find a critical behavior of inertia for small Stokes values. Starting from the pure monodisperse statistics we also characterize polydisperse suspensions with a given mean Stokes, (St) over bar.