WS1-3 Mean settling velocity and turbulent dispersion of fine solid particles in nearly isotropic turbulence generated by spinning grids.(2)

2006 ◽  
Vol 2006 (0) ◽  
pp. _WS1-3-1_-_WS1-3-4_
Author(s):  
Tatsuo USHIJIMA
Keyword(s):  
Settling Velocity ◽  
Isotropic Turbulence ◽  
Solid Particles ◽  
Turbulent Dispersion

Effect of Reynolds Number on Isotropic Turbulent Dispersion

1995 ◽  
Vol 117 (3) ◽  
pp. 402-409 ◽  
Author(s):  
Renwei Mei ◽  
Ronald J. Adrian
Keyword(s):  
Reynolds Number ◽  
Settling Velocity ◽  
Isotropic Turbulence ◽  
Temporal Structure ◽  
Turbulent Dispersion ◽  
Turbulence Structure ◽  
Auto Correlation ◽  
Auto Correlation Function ◽  
Spatio Temporal ◽  
Spectrum Model

The influence of the spatio-temporal structure of isotropic turbulence on the dispersion of fluid and particles with inertia is investigated. The spatial structure is represented by an extended von Ka´rma´n energy spectrum model which includes an inertial sub-range and allows evaluation of the effect of the turbulence Reynolds number, Reλ. Dispersion of fluid is analyzed using four different models for the Eulerian temporal auto-correlation function D(τ). The fluid diffusivity, normalized by the integral length scale L11 and the root-mean-square turbulent velocity u0, depends on Reλ. The parameter cE = T0u0/L11, in which T0 is the Eulerian integral time scale, has commonly been assumed to be constant. It is shown that cE strongly affects the value of the fluid diffusivity. The dispersion of a particle with finite inertia and finite settling velocity is analyzed for a large range of a particle inertia and settling velocity. Particle turbulence intensity and diffusivity are influenced strongly by turbulence structure.

Kinetic Approach for Solid Inertial Particle Deposition in Turbulent Near-Wall Region Flow Lattice Boltzmann Based Numerical Resolution

2011 ◽  
Author(s):  
E. Diounou ◽  
P. Fede ◽  
R. Fournier ◽  
S. Blanco ◽  
O. Simonin
Keyword(s):  
Random Walk ◽  
Kinetic Equation ◽  
Lattice Boltzmann ◽  
Particle Deposition ◽  
Isotropic Turbulence ◽  
Solid Particles ◽  
Wall Region ◽  
Inertial Particles ◽  
Two Phase ◽  
Numerical Resolution

The purpose of the paper is the deposition on the wall of inertial solid particles suspended in turbulent flow. The modeling of such a system is based on a statistical description using a Probability Density Function. In the PDF transport equation, an original model proposed Aguinaga et al. (2009) is used to close the term representing the fluid-particle interactions. The resulting kinetic equation may be difficult to solve especially in the case of the particle response time is smaller than the integral time scale of the turbulence. In the present paper, the Lattice Boltzmann Method is used in order to overcome such numerical problems. The accuracy of the method and its ability to solve the two-phase kinetic equation is analyzed in the simple case of inertial particles in homogeneous isotropic turbulence for which Lagrangian random walk simulation results are available. The results from LBM are in accordance with the random walk simulations.

scholarly journals Can terminal settling velocity and drag of natural particles in water ever be predicted accurately?

2020 ◽  
Author(s):  
Onno J. I. Kramer ◽  
Peter J. de Moel ◽  
Shravan K. R. Raaghav ◽  
Eric T. Baars ◽  
Wim H. van Vugt ◽  
...  
Keyword(s):  
Drinking Water ◽  
Measurement Errors ◽  
Settling Velocity ◽  
Particle Density ◽  
Fixed Bed ◽  
Drinking Water Treatment ◽  
Liquid System ◽  
Solid Particles ◽  
Spherical Particles ◽  
Fluidised Bed

Abstract. Natural particles are frequently applied in drinking water treatment processes in fixed bed reactors, in fluidised bed reactors, and in sedimentation processes to clarify water and to concentrate solids. When particles settle, it has been found that in terms of hydraulics, natural particles behave differently when compared to perfectly round spheres. To estimate the terminal settling velocity of single solid particles in a liquid system, a comprehensive collection of equations is available. For perfectly round spheres, the settling velocity can be calculated quite accurately. However, for naturally polydisperse non-spherical particles, experimentally measured settling velocities of individual particles show considerable spread from the calculated average values. This work aimed to analyse and explain the different causes of this spread. To this end, terminal settling experiments were conducted in a quiescent fluid with particles varying in density, size and shape. For the settling experiments, opaque and transparent spherical polydisperse and monodisperse glass beads were selected. In this study, we also examined drinking water related particles, like calcite pellets and crushed calcite seeding material grains, both applied in drinking water softening. Polydisperse calcite pellets were sieved and separated to acquire more uniformly dispersed samples. In addition, a wide variety of grains with different densities, sizes and shapes were investigated for their terminal settling velocity and behaviour. The derived drag coefficient was compared with well-known models such as Brown–Lawler. A sensitivity analysis showed that the spread is caused to a lesser extent by variations in fluid properties, measurement errors and wall effects. Natural variations in specific particle density, path trajectory instabilities and distinctive multi-particle settling behaviour caused a slightly larger degree of spread. In contrast, greater spread is caused by variations in particle size, shape and orientation.

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.

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