The settling velocity of heavy particles in an aqueous near-isotropic turbulence

2003 ◽  
Vol 15 (4) ◽  
pp. 868-880 ◽  
Author(s):  
T. S. Yang ◽  
S. S. Shy
Keyword(s):  
Settling Velocity ◽  
Isotropic Turbulence ◽  
Heavy Particles

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.

Settling velocity and concentration distribution of heavy particles in homogeneous isotropic turbulence

1993 ◽  
Vol 256 ◽  
pp. 27-68 ◽  
Author(s):  
Lian-Ping Wang ◽  
Martin R. Maxey
Keyword(s):  
Numerical Simulations ◽  
Drag Force ◽  
Settling Velocity ◽  
Isotropic Turbulence ◽  
Concentration Field ◽  
Terminal Velocity ◽  
Direct Numerical Simulations ◽  
Flow Dynamics ◽  
Homogeneous Turbulence ◽  
Heavy Particles

The average settling velocity in homogeneous turbulence of a small rigid spherical particle, subject to a Stokes drag force, has been shown to differ from that in still fluid owing to a bias from the particle inertia (Maxey 1987). Previous numerical results for particles in a random flow field, where the flow dynamics were not considered, showed an increase in the average settling velocity. Direct numerical simulations of the motion of heavy particles in isotropic homogeneous turbulence have been performed where the flow dynamics are included. These show that a significant increase in the average settling velocity can occur for particles with inertial response time and still-fluid terminal velocity comparable to the Kolmogorov scales of the turbulence. This increase may be as much as 50% of the terminal velocity, which is much larger than was previously found. The concentration field of the heavy particles, obtained from direct numerical simulations, shows the importance of the inertial bias with particles tending to collect in elongated sheets on the peripheries of local vortical structures. This is coupled then to a preferential sweeping of the particles in downward moving fluid. Again the importance of Kolmogorov scaling to these processes is demonstrated. Finally, some consideration is given to larger particles that are subject to a nonlinear drag force where it is found that the nonlinearity reduces the net increase in settling velocity.

scholarly journals Settling Velocity of Microplastics Exposed to Wave Action

2021 ◽  
Vol 9 (2) ◽  
pp. 142
Author(s):  
Annalisa De Leo ◽  
Laura Cutroneo ◽  
Damien Sous ◽  
Alessandro Stocchino
Keyword(s):  
Laboratory Experiments ◽  
Settling Velocity ◽  
Transport Model ◽  
Stokes Drift ◽  
Inertial Effects ◽  
Sea Waves ◽  
Heavy Particles ◽  
Analytical Formulation ◽  
Simplified Approach ◽  
Remote Areas

Microplastic (MP) debris is recognized to be one of the most serious threats to marine environments. They are found in all seas and oceanic basins worldwide, even in the most remote areas. This is further proof that the transport of MPs is very efficient. In the present study, we focus our attention on MPs’ transport owing to the Stokes drift generated by sea waves. Recent studies have shown that the interaction between heavy particles and Stokes drift leads to unexpected phenomena mostly related to inertial effects. We perform a series of laboratory experiments with the aim to directly measure MPs’ trajectories under different wave conditions. The main objective is to quantify the inertial effect and, ultimately, suggest a new analytical formulation for the net settling velocity. The latter formula might be implemented in a larger scale transport model in order to account for inertial effects in a simplified approach.

Acceleration of heavy particles in isotropic turbulence

2008 ◽  
Vol 34 (9) ◽  
pp. 865-868 ◽  
Author(s):  
Leonid I. Zaichik ◽  
Vladimir M. Alipchenkov
Keyword(s):  
Isotropic Turbulence ◽  
Heavy Particles

scholarly journals Formulation of the Settling Velocity of Small Particles Initially Situated inside an Inclined Vortex

2016 ◽  
Vol 2016 ◽  
pp. 1-8
Author(s):  
Urbano Sánchez
Keyword(s):  
Settling Velocity ◽  
Three Dimensional ◽  
Particle Diameter ◽  
Particle Separation ◽  
Small Particles ◽  
Theoretical Formulation ◽  
Heavy Particles ◽  
Elapsed Time ◽  
Escape Process ◽  
Separation Devices

Both the estimation of the time that small heavy particles remain inside a 3D vortex and the estimation of the average settling velocity of those particles are some important features in many practical situations. Previous works focused on the case of a horizontal 2D vortex. In this paper, we simulate the dynamics of heavy particles initially situated inside a three-dimensional vortex obtaining a formula for their average settling velocity. In a previous paper we obtained the trajectories of the particles and a formula that provides the time that they need to escape,Te⁎. This work simulates and analyses the escape process, and its main result is the obtaining, from numerical simulation, of a theoretical formulation of the average settling velocityVz⁎and its relationship with the elapsed time. We prove that the permanence time is of the order ofdp⁎-10(withdp⁎particle diameter) and that the average settling velocity is of the order ofTe⁎-1/5for sufficiently small particles. Some applications of the settling velocity formula developed in this work would be the design of mixture devices, the design of particle separation devices, and the prediction of the settling of pollutant particles, seeds, and pollen.

Turbulent Dispersion of Heavy Particles With Nonlinear Drag

1997 ◽  
Vol 119 (1) ◽  
pp. 170-179 ◽  
Author(s):  
Renwei Mei ◽  
R. J. Adrian ◽  
T. J. Hanratty
Keyword(s):  
Isotropic Turbulence ◽  
Fluid Velocity ◽  
Interpolation Formula ◽  
Mean Value ◽  
Particle Dispersion ◽  
Turbulent Dispersion ◽  
Heavy Particles ◽  
Time Constants ◽  
The Mean ◽  
Drag Law

The analysis of Reeks (1977) for particle dispersion in isotropic turbulence is extended so as to include a nonlinear drag law. The principal issue is the evaluation of the inertial time constants, βα−1, and the mean slip. Unlike what is found for the Stokesian drag, the time constants are functions of the slip velocity and are anisotropic. For settling velocity, VT, much larger than root-mean-square of the fluid velocity fluctuations, u0, the mean slip is given by VT. For VT→0, the mean slip is related to turbulent velocity fluctuation by assuming that fluctuations in βα are small compared to the mean value. An interpolation formula is used to evaluate βα and VT in regions intermediate between conditions of VT→0 and VT≫ u0. The limitations of the analysis are explored by carrying out a Monte-Carlo simulation for particle motion in a pseudo turbulence described by a Gaussian distribution and Kraichnan’s (1970) energy spectrum.

scholarly journals Modelling of turbulence modulation in particle- or droplet-laden flows

2012 ◽  
Vol 706 ◽  
pp. 251-273 ◽  
Author(s):  
Daniel W. Meyer
Keyword(s):  
Isotropic Turbulence ◽  
Density Ratio ◽  
Joint Probability ◽  
Stokes Number ◽  
Navier Stokes ◽  
Grid Turbulence ◽  
Heavy Particles ◽  
Turbulence Modulation ◽  
Modelling Framework ◽  
Liquid Flows

AbstractAddition of particles or droplets to turbulent liquid flows or addition of droplets to turbulent gas flows can lead to modulation of turbulence characteristics. Corresponding observations have been reported for very small particle or droplet volume loadings ${\Phi }_{v} $ and therefore may be important when simulating such flows. In this work, a modelling framework that accounts for preferential concentration and reproduces isotropic and anisotropic turbulence attenuation effects is presented. The framework is outlined for both Reynolds-averaged Navier–Stokes (RANS) and joint probability density function (p.d.f.) methods. Validations are performed involving a range of particle and flow-field parameters and are based on the direct numerical simulation (DNS) study of Boivin, Simonin & Squires (J. Fluid Mech., vol. 375, 1998, pp. 235–263) dealing with heavy particles suspended in homogeneous isotropic turbulence (Stokes number $\mathit{St}= O(1{\unicode{x2013}} 10)$, particle/fluid density ratio ${\rho }_{p} / \rho = 2000$, ${\Phi }_{v} = O(1{0}^{- 4} )$) and the experimental investigation of Poelma, Westerweel & Ooms (J. Fluid Mech., vol. 589, 2007, pp. 315–351) involving light particles ($\mathit{St}= O(0. 1)$, ${\rho }_{p} / \rho \gtrsim 1$, ${\Phi }_{v} = O(1{0}^{- 3} )$) settling in grid turbulence. The development in this work is restricted to volume loadings where particle or droplet collisions are negligible.

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