Spatial distributions of heavy particles suspended in an incompressible isotropic and homogeneous turbulent flow are investigated by means high resolution direct numerical simulations. In the dissipative range, it is shown that form fractal clusters with properties independent Reynolds number. Clustering there optimal when particle response time order Kolmogorov scale tau(eta). inertial distribution no longer invariant. It is, however, deviations from uniformity depend on a rescaled...

We present the results of Direct Numerical Simulations (DNS) turbulent flows seeded with millions passive inertial particles. The maximum Taylor's Reynolds number is around 200. consider particles much heavier than carrier flow in limit when Stokes drag force dominates their dynamical evolution. discuss both transient and stationary regimes. In regime, we study growt inhomogeneities particle spatial distribution driven by preferential concentration out intense vortex filaments. acceleration...

We study the statistical properties of homogeneous and isotropic three-dimensional (3D) turbulent flows. By introducing a novel way to make numerical investigations Navier-Stokes equations, we show that all 3D flows in nature possess subset nonlinear evolution leading reverse energy transfer: from small large scales. Up now, such an inverse cascade was only observed under strong rotation quasi-two-dimensional geometries confinement. here flux is always reversed when mirror symmetry broken,...

We present the results of direct numerical simulations heavy particle transport in homogeneous, isotropic, fully developed turbulence, up to resolution $512^3$ ($R_\lambda\approx 185$). Following trajectories 120 million particles with Stokes numbers, $St$, range from 0.16 3.5 we are able characterize full detail statistics acceleration. show that: ({\it i}) The root-mean-squared acceleration $a_{\rm rms}$ sharply falls off fluid tracer value already at quite small numbers; ii}) At a given...

Statistical features of homogeneous, isotropic, two-dimensional turbulence is discussed on the basis a set direct numerical simulations up to unprecedented resolution $32768^2$. By forcing system at intermediate scales, narrow but clear inertial ranges develop both for inverse and cascades where two Kolmogorov laws structure functions are, first time, simultaneously observed. The cascade spectrum found be consistent with Kolmogorov-Kraichnan prediction robust respect presence an enstrophy...

We investigate the behavior of turbulent systems in geometries with one compactified dimension. A novel phenomenological scenario dominated by splitting cascade emerges both from theoretical analysis passive scalar turbulence and direct numerical simulations Navier-Stokes turbulence.

Abstract We investigate the transfer properties of energy and helicity fluctuations in fully developed homogeneous isotropic turbulence by changing nature nonlinear Navier–Stokes terms. perform a surgery all possible interactions, keeping only those triads that have sign-definite content. In order to do this, we apply an exact decomposition velocity field helical Fourier basis, as first proposed Constantin & Majda ( Commun. Math. Phys , vol. 115, 1988, p. 435) exploited great detail...

By using direct numerical simulations (DNS) at unprecedented resolution we study turbulence under rotation in the presence of simultaneous and inverse cascades. The accumulation energy large scale leads to formation vertical coherent regions with high vorticity oriented along axis. seeding flow millions inertial particles, quantify -for first time- effects those structures on preferential concentration light heavy particles. Furthermore, quantitatively show that extreme fluctuations, leading...

In this work we investigate, by means of direct numerical hyperviscous simulations, how rotation affects the bidimensionalization a turbulent flow. We study thin layer fluid, forced two-dimensional forcing, within framework ``split cascade'' in which injected energy flows both to small scales (generating cascade) and large scale (to form inverse cascade). It is shown that reinforces cascade at expense one, thus promoting This achieved suppression enstrophy production scales. Nonetheless,...

We report numerical evidence of elastic turbulence phenomenology in a two-dimensional periodic Kolmogorov flow. By direct simulations the Oldroyd-B viscoelastic model at very small Reynolds numbers, we find that above instability threshold flow develops an turbulent regime. observe both drag and Lyapunov exponent increase with Weissenberg number, indicating presence disordered, turbulentlike mixing The energy spectrum power-law scaling range close to experimental theoretical expectations.

Finite-size impurities suspended in incompressible flows distribute inhomogeneously, leading to a drastic enhancement of collisions. A description the dynamics full position-velocity phase space is essential understand underlying mechanisms, especially for polydisperse suspensions. These issues are studied here particles much heavier than fluid by means Lagrangian approach. It shown that inertia enhances collision rates through two effects: correlation among particle positions induced...

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

The Rayleigh--Taylor (RT) turbulence is investigated by means of high resolution numerical simulations. main question addressed here on whether RT phenomenology can be considered as a manifestation universality Navier--Stokes equations with respect to forcing mechanisms. At theoretical level the situation far from being firmly established and, indeed, contrasting predictions have been formulated. Our first aim clarify above controversy through deep analysis scaling behavior relevant...

Abstract We investigate the statistical properties of Rayleigh–Taylor turbulence in a three-dimensional convective cell high aspect ratio, which one transverse side is much smaller that others. By means high-resolution numerical simulation we study development turbulent mixing layer and scaling velocity temperature fields. show system undergoes transition from three- to two-dimensional regime when width becomes larger than scale confinement. In late stage evolution flow characterized by...

We study the chaoticity and predictability of a turbulent flow on basis high-resolution direct numerical simulations at different Reynolds numbers. find that Lyapunov exponent turbulence, which measures exponential separation two initially close solutions Navier-Stokes equations, grows with number flow, an anomalous scaling exponent, larger than one obtained dimensional grounds. For large perturbations, error is transferred to larger, slower scales, where it algebraically generating "inverse...

Numerical simulations of a thin layer turbulent flow in stably stratified conditions within the Boussinesq approximation have been performed. The statistics energy transfer among scales investigated for different values control parameters: thickness and density stratification. It is shown that with quasi-two-dimensional phenomenology, stratification provides new channel towards small reduces inverse cascade. role vortex stretching enstrophy flux kinetic into potential at discussed.

We discuss the phenomenology of split energy cascade in a three-dimensional thin fluid layer by mean high resolution numerical simulations Navier-Stokes equations. observe presence both an inverse at large scales, as predicted for two-dimensional turbu- lence, and direct small turbulence. The is associated with enstrophy intermediate range scales. Notably, we find that this system not pure 2D phenomenon, coupling 3D velocity field necessary to guarantee constancy fluxes.

We study the transition from momentum- to buoyancy-dominated regime in temporal jets forced by gravity. From conservation of thermal content and volume flux, we develop a simple model which is able describe accurately between two regimes terms single parameter representing entrainment coefficient. Our analytical results are validated against set numerical simulations planar plumes at different initial values Reynolds Froude numbers. find that, although pure jet-scaling law not clearly...

We study the statistics of vorticity field in two-dimensional Navier-Stokes turbulence with a linear Ekman friction. show that small-scale fluctuations are intermittent, as conjectured by Nam et al. [Phys. Rev. Lett. vol.84 (2000) 5134]. The coincides one passive scalar finite lifetime transported velocity itself.

We study the direct enstrophy cascade in a two-dimensional flow generated an electromagnetically driven thin layer of fluid. Due to presence bottom friction, energy spectrum deviates from classical Kraichnan prediction k−3. find that correction spectral slope depends on thickness layer, agreement with theoretical based analogy passive scalar statistics.

Three-dimensional numerical simulations of forced turbulence in a thin layer show the transfer from forcing to larger scales is by two-dimensional modes, and smaller three-dimensional latter providing viscosity-independent dissipation.

We investigate theoretically and numerically the effect of polymer additives on two-dimensional turbulence by means a viscoelastic model. provide compelling evidence that at vanishingly small concentrations, such polymers are passively transported, probability distribution elongation has power law tail: its slope is related to statistics finite-time Lyapunov exponents flow, in quantitative agreement with theoretical predictions. show finite concentrations sufficiently large elasticity react...

We study the effects of polymer additives on turbulence generated by ubiquitous Rayleigh-Taylor instability. Numerical simulations complete viscoelastic models provide clear evidence that heat transport is enhanced up to 50% with respect Newtonian case. This phenomenon accompanied a speed mixing layer growth. give phenomenological interpretation these results based small-scale turbulent reduction induced polymers.

The Kolmogorov flow provides an ideal instance of a virtual channel flow: It has no boundaries, but nevertheless it possesses well defined mean in each half-wavelength. We exploit this remarkable feature for the purpose investigating interplay between and turbulent drag bulk flow. By means set direct numerical simulations at increasing Reynolds number we show dependence on amplitude Further, present detailed analysis scale-by-scale energy balance, which describes how kinetic is redistributed...