Antonino Ferrante

On the physical mechanisms of two-way coupling in particle-laden isotropic turbulence

The objective of the present study is to analyze our recent direct numerical simulation (DNS) results to explain in some detail the main physical mechanisms responsible for the modification of isotropic turbulence by dispersed solid particles. The details of these two-way coupling mechanisms have not been explained in earlier publications. The present study, in comparison to the previous DNS studies, has been performed with higher resolution (Reλ=75) and considerably larger number (80 million) of particles, in addition to accounting for the effects of gravity. We study the modulation of turbulence by the dispersed particles while fixing both their volume fraction, φv=10−3, and mass fraction, φm=1, for three different particles classified by the ratio of their response time to the Kolmogorov time scale: microparticles, τp/τk≪1, critical particles, τp/τk≈1, large particles, τp/τk>1. Furthermore, we show that in zero gravity, dispersed particles with τp/τk=0.25 (denoted here as “ghost particles”) modify the ...

Modulation of isotropic turbulence by particles of Taylor length-scale size

This study investigates the two-way coupling effects of finite-size solid spherical particles on decaying isotropic turbulence using direct numerical simulation with an immersed boundary method. We fully resolve all the relevant scales of turbulence around freely moving particles of the Taylor length-scale size, 1.2≤d/λ≤2.6. The particle diameter and Stokes number in terms of Kolmogorov length- and time scales are 16≤d/η≤35 and 38≤τp/τk≤178, respectively, at the time the particles are released in the flow. The particles mass fraction range is 0.026≤φm≤1.0, corresponding to a volume fraction of 0.01≤φv≤0.1 and density ratio of 2.56≤ρp/ρf≤10. The maximum number of dispersed particles is 6400 for φv=0.1. The typical particle Reynolds number is of O(10). The effects of the particles on the temporal development of turbulence kinetic energy E(t), its dissipation rate (t), its two-way coupling rate of change Ψp(t) and frequency spectra E(ω) are discussed.In contrast to particles with d η, is that E(t) is always smaller than that of the single-phase flow. In addition, Ψp(t) is always positive for particles with d > η, whereas it can be positive or negative for particles with d < η.

On the physical mechanisms of drag reduction in a spatially developing turbulent boundary layer laden with microbubbles

The objective of this paper is to explain, in as much detail as possible, the physical mechanisms responsible for the reduction of skin friction in a microbubble-laden spatially developing turbulent boundary layer over a flat plate, for

Reynolds number effect on drag reduction in a microbubble-laden spatially developing turbulent boundary layer

Re_{\theta} = 1430

A fast pressure-correction method for incompressible two-fluid flows

. Our DNS results with microbubble volume fraction ranging from

LES of an inclined sonic jet into a turbulent crossflow at Mach 3.6

\phi_v = 0.001

On the effects of microbubbles on Taylor–Green vortex flow

to 0.02 show that the presence of bubbles results in a local positive divergence of the fluid velocity,

On the accuracy of the two-fluid formulation in direct numerical simulation of bubble-laden turbulent boundary layers

{\bm \nabla} \,{\bm \cdot}\,{\bm U} > 0

Analytical Model of the Time Developing Turbulent Boundary Layer

, creating a positive mean velocity normal to (and away from) the wall which, in turn, reduces the mean streamwise velocity and displaces the quasi-streamwise longitudinal vortical structures away from the wall. This displacement has two main effects: (i) it increases the spanwise gaps between the wall streaks associated with the sweep events and reduces the streamwise velocity in these streaks, thus reducing the skin friction by up to 20.2% for

A robust method for generating inflow conditions for direct simulations of spatially-developing turbulent boundary layers

\phi_v = 0.02