Federico Toschi

Generalized lattice Boltzmann method with multirange pseudopotential.

The physical behavior of a class of mesoscopic models for multiphase flows is analyzed in details near interfaces. In particular, an extended pseudopotential method is developed, which permits to tune the equation of state and surface tension independently of each other. The spurious velocity contributions of this extended model are shown to vanish in the limit of high grid refinement and/or high order isotropy. Higher order schemes to implement self-consistent forcings are rigorously computed for 2d and 3d models. The extended scenario developed in this work clarifies the theoretical foundations of the Shan-Chen methodology for the lattice Boltzmann method and enhances its applicability and flexibility to the simulation of multiphase flows to density ratios up to O(100).

Dynamics and statistics of heavy particles in turbulent flows

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 λ∼ 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 ∈ [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, .

Acceleration statistics of heavy particles in turbulence

We present the results of direct numerical simulations of heavy particle transport in homogeneous, isotropic, fully developed turbulence, up to resolution

Shear-improved Smagorinsky model for large-eddy simulation of wall-bounded turbulent flows

512^3

Particle trapping in three-dimensional fully developed turbulence

(

Mesoscopic modeling of a two-phase flow in the presence of boundaries: The contact angle

R_\lambda\approx 185

Acceleration and vortex filaments in turbulence

). 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

Universal intermittent properties of particle trajectories in highly turbulent flows

a_{\rm rms}

The effect of microbubbles on developed turbulence

sharply falls off from the fluid tracer value at quite small Stokes numbers; (ii) at a given St the normalized acceleration

Rotation Rate of Rods in Turbulent Fluid Flow

a_{\rm rms}/(\epsilon^3/\nu)^{1/4}