Pair dispersion and preferential concentration of particles in isotropic turbulence

2003 ◽  
Vol 15 (6) ◽  
pp. 1776 ◽  
Author(s):  
Leonid I. Zaichik ◽  
Vladimir M. Alipchenkov
Keyword(s):  
Isotropic Turbulence ◽  
Preferential Concentration

Particle Dispersion in Fine Scales of Homogeneous Isotropic Turbulence

2007 ◽  
Author(s):  
M. Sato ◽  
M. Tanahashi ◽  
T. Miyauchi
Keyword(s):  
Isotropic Turbulence ◽  
Major Axis ◽  
Stokes Number ◽  
High Energy ◽  
Energy Dissipation Rate ◽  
Particle Dispersion ◽  
Fine Scale ◽  
Number Density ◽  
Homogeneous Isotropic Turbulence ◽  
Preferential Concentration

Direct numerical simulations of homogeneous isotropic turbulence laden with particles have been conducted to clarify the relationship between particle dispersion and coherent fine scale eddies in turbulence. Dispersion of 106 particles are analyzed for several particle Stokes numbers. The spatial distributions of particles depend on their Stokes number, and the Stokes number that causes preferential concentration of particles is closely related to the time scale of coherent fine scale eddies in turbulence. On the plane perpendicular to the rotating axes of fine scale eddies, number density of particle with particular Stokes number is low at the center of the fine scale eddy, and high in the regions with high energy dissipation rate around the eddy. The maximum number density can be observed at about 1.5 to 2.0 times the eddy radius on the major axis of the fine scale eddy.

Effect of preferential concentration on the settling velocity of heavy particles in homogeneous isotropic turbulence

2002 ◽  
Vol 468 ◽  
pp. 77-105 ◽  
Author(s):  
A. ALISEDA ◽  
A. CARTELLIER ◽  
F. HAINAUX ◽  
J. C. LASHERAS
Keyword(s):  
Settling Velocity ◽  
Isotropic Turbulence ◽  
Volume Fraction ◽  
Concentration Field ◽  
Temporal Distribution ◽  
Local Concentration ◽  
Heavy Particles ◽  
Flow Measurements ◽  
Preferential Concentration ◽  
Decaying Turbulence

The behaviour of heavy particles in isotropic, homogeneous, decaying turbulence has been experimentally studied. The settling velocity of the particles has been found to be much larger than in a quiescent fluid. It has been determined that the enhancement of the settling velocity depends on the particle loading, increasing as the volume fraction of particles in the flow increases. The spatial and temporal distribution of the particle concentration field is shown to exhibit large inhomogeneities. As the particles interact with the underlying turbulence they concentrate preferentially in certain regions of the flow. A characteristic dimension of these particle clusters is found to be related to the viscous scales of the flow. Measurements of the settling velocity conditioned on the local concentration of particles in the flow have shown that there is a monotonic increase in the settling velocity with the local concentration (the relation being quasi-linear). A simple phenomenological model is proposed to explain this behaviour.

Direct numerical simulation of turbulence modulation by particles in compressible isotropic turbulence

2017 ◽  
Vol 832 ◽  
pp. 438-482 ◽  
Author(s):  
Qi Dai ◽  
Kun Luo ◽  
Tai Jin ◽  
Jianren Fan
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Rotational Motion ◽  
Isotropic Turbulence ◽  
Volume Fraction ◽  
Stokes Number ◽  
Systematic Investigation ◽  
Turbulence Modulation ◽  
Physical Mechanisms ◽  
Preferential Concentration

In this paper, a systematic investigation of turbulence modulation by particles and its underlying physical mechanisms in decaying compressible isotropic turbulence is performed by using direct numerical simulations with the Eulerian–Lagrangian point-source approach. Particles interact with turbulence through two-way coupling and the initial turbulent Mach number is 1.2. Five simulations with different particle diameters (or initial Stokes numbers, $St_{0}$) are conducted while fixing both their volume fraction and particle densities. The underlying physical mechanisms responsible for turbulence modulation are analysed through investigating the particle motion in the different cases and the transport equations of turbulent kinetic energy, vorticity and dilatation, especially the two-way coupling terms. Our results show that microparticles ($St_{0}\leqslant 0.5$) augment turbulent kinetic energy and the rotational motion of fluid, critical particles ($St_{0}\approx 1.0$) enhance the rotational motion of fluid, and large particles ($St_{0}\geqslant 5.0$) attenuate turbulent kinetic energy and the rotational motion of fluid. The compressibility of the turbulence field is suppressed for all the cases, and the suppression is more significant if the Stokes number of particles is close to 1. The modifications of turbulent kinetic energy, the rotational motion and the compressibility are all related with the particle inertia and distributions, and the suppression of the compressibility is attributed to the preferential concentration and the inertia of particles.

Preferential concentration of heavy particles in compressible isotropic turbulence

2016 ◽  
Vol 28 (5) ◽  
pp. 055104 ◽  
Author(s):  
Qingqing Zhang ◽  
Han Liu ◽  
Zongqiang Ma ◽  
Zuoli Xiao
Keyword(s):  
Isotropic Turbulence ◽  
Heavy Particles ◽  
Preferential Concentration

Lift Force Effects on the Behavior of Bubbles in Homogeneous Isotropic Turbulence

2005 ◽  
Author(s):  
Mustapha Abbad ◽  
Benoiˆt Oesterle´
Keyword(s):  
Relative Velocity ◽  
Lift Force ◽  
Isotropic Turbulence ◽  
Stokes Number ◽  
Rise Velocity ◽  
Homogeneous Isotropic Turbulence ◽  
Preferential Concentration ◽  
Coupling Approximation ◽  
Lagrangian Tracking ◽  
Small Bubbles

The influence of lift forces on the dispersion of small bubbles is numerically studied in a homogeneous isotropic turbulence generated by random Fourier modes, under one-way coupling approximation. The effects of bubble Stokes number and mean relative velocity are investigated by computing the statistics from Lagrangian tracking of a large number of bubbles in many flow field realizations, and comparison is provided between the results obtained with and without taking the lift force into account. The effects of preferential concentration, which are known to reduce the terminal rise velocity of bubbles, are also investigated. The lift force is found to drastically modify the correlations and integral time scales of the fluid seen by the bubbles in their fluctuating motion, and to significantly enhance the accumulation of bubbles in high vorticity regions.

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