Turbulent Clustering of Point Particles and Finite-Size Particles in Isotropic Turbulent Flows

2013 ◽  
Vol 52 (33) ◽  
pp. 11294-11301 ◽  
Author(s):  
Guodong Jin ◽  
Yun Wang ◽  
Jian Zhang ◽  
Guowei He
Keyword(s):  
Turbulent Flows ◽  
Finite Size ◽  
Point Particles

Improved Discrete Random Walk Stochastic Model for Simulating Particle Dispersion and Deposition in Inhomogeneous Turbulent Flows

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Amir A. Mofakham ◽  
Goodarz Ahmadi
Keyword(s):  
Random Walk ◽  
Turbulent Flows ◽  
Particle Deposition ◽  
Finite Size ◽  
Particle Dispersion ◽  
Concentration Profiles ◽  
Velocity Fluctuations ◽  
Point Particles ◽  
Deposition Velocities ◽  
Gradient Drift

Abstract The performance of different versions of the discrete random walk models in turbulent flows with nonuniform normal root-mean-square (RMS) velocity fluctuations and turbulence time scales were carefully investigated. The OpenFOAM v2−f low Reynolds number turbulence model was used for evaluating the fully developed streamwise velocity and the wall-normal RMS velocity fluctuations profiles in a turbulent channel flow. The results were then used in an in-house matlab particle tracking code, including the drag and Brownian forces, and the trajectories of randomly injected point-particles with diameters ranging from 10 nm to 30 μm were evaluated under the one-way coupling assumption. The distributions and deposition velocities of fluid-tracer and finite-size particles were evaluated using the conventional-discrete random walk (DRW) model, the modified-DRW model including the velocity gradient drift correction, and the new improved-DRW model including the velocity and time gradient drift terms. It was shown that the conventional-DRW model leads to superfluous migration of fluid-point particles toward the wall and erroneous particle deposition rate. The concentration profiles of tracer particles obtained by using the modified-DRW model still are not uniform. However, it was shown that the new improved-DRW model with the velocity and time scale drift corrections leads to uniform distributions for fluid-point particles and reasonable concentration profiles for finite-size heavy particles. In addition, good agreement was found between the estimated deposition velocities of different size particles by the new improved-DRW model with the available data.

Lagrangian frequency spectra of vertical velocity and vorticity in high-Reynolds-number oceanic turbulence

1998 ◽  
Vol 362 ◽  
pp. 177-198 ◽  
Author(s):  
REN-CHIEH LIEN ◽  
ERIC A. D'ASARO ◽  
GEOFFREY T. DAIRIKI
Keyword(s):  
Turbulent Flows ◽  
Frequency Spectrum ◽  
Finite Size ◽  
Inertial Subrange ◽  
Substantial Part ◽  
Spatial Average ◽  
Vertical Acceleration ◽  
Frequency Range ◽  
Frequency Spectra ◽  
Large Eddy

Lagrangian properties of oceanic turbulent boundary layers were measured using neutrally buoyant floats. Vertical acceleration was computed from pressure (depth) measured on the floats. An average vertical vorticity was computed from the spin rate of the float. Forms for the Lagrangian frequency spectra of acceleration, ϕa(ω), and the Lagrangian frequency spectrum of average vorticity are found using dimension analysis. The flow is characterized by a kinetic energy dissipation rate, ε, and a large-eddy frequency, ω0. The float is characterized by its size. The proposed non-dimensionalization accurately collapses the observed spectra into a common form. The spectra differ from those expected for perfect Lagrangian measurements over a substantial part of the measured frequency range owing to the finite size of the float. Exact theoretical forms for the Lagrangian frequency spectra are derived from the corresponding Eulerian wavenumber spectra and a wavenumber–frequency distribution function used in previous numerical simulations of turbulence. The effect of finite float size is modelled as a spatial average. The observed non-dimensional acceleration and vorticity spectra agree with these theoretical predictions, except for the high-frequency part of the vorticity spectrum, where the details of the float behaviour are important, but inaccurately modelled. A correction to the exact Lagrangian acceleration spectra due to measurement by a finite-sized float is thus obtained. With this correction, a frequency range extending from approximately one decade below ω0 to approximately one decade into the inertial subrange can be resolved by the data. Overall, the data are consistent with the proposed transformation from the Eulerian wavenumber spectrum to the Lagrangian frequency spectrum. Two parameters, ε and ω0, are sufficient to describe Lagrangian spectra from several different oceanic turbulent flows. The Lagrangian Kolmogorov constant for acceleration, βa≡ϕa/ε, has a value between 1 and 2 in a convectively driven boundary layer. The analysis suggests a Lagrangian frequency spectrum for vorticity that is white at all frequencies in the inertial subrange and below, and a Lagrangian frequency spectrum for energy that is white below the large-eddy scale and has a slope of −2 in the inertial subrange.

DISTRIBUTIONAL TORSION OF COSMIC STRINGS WITH POLARIZED SPINNING MATTER

1998 ◽  
Vol 13 (27) ◽  
pp. 2227-2230 ◽  
Author(s):  
L. C. GARCIA DE ANDRADE
Keyword(s):  
Angular Momentum ◽  
Cosmic String ◽  
Cosmic Strings ◽  
Finite Size ◽  
The Other ◽  
Spinning Particles ◽  
Point Particles ◽  
Cartan Torsion ◽  
Spin Polarized ◽  
Dirac Distribution

A cosmic string of finite size in Weitzenböck space–time is built where spin polarized particles can be found along the string and orthogonal to it. Only spinning particles polarized along the string contribute to the angular momentum of the string while the other is only a torsion source like in Einstein–Cartan (EC) theory. Cartan torsion is given by a δ-Dirac distribution and the metric is the lift of (2+1)-gravity point particles to (3+1)-cosmic strings.

scholarly journals New class of turbulence in active fluids

2015 ◽  
Vol 112 (49) ◽  
pp. 15048-15053 ◽  
Author(s):  
Vasil Bratanov ◽  
Frank Jenko ◽  
Erwin Frey
Keyword(s):  
Turbulent Flows ◽  
Stokes Equations ◽  
Spatial Scales ◽  
Finite Size ◽  
Power Laws ◽  
Theoretical Work ◽  
Navier Stokes ◽  
Physical Parameters ◽  
New Class ◽  
General Terms

Turbulence is a fundamental and ubiquitous phenomenon in nature, occurring from astrophysical to biophysical scales. At the same time, it is widely recognized as one of the key unsolved problems in modern physics, representing a paradigmatic example of nonlinear dynamics far from thermodynamic equilibrium. Whereas in the past, most theoretical work in this area has been devoted to Navier–Stokes flows, there is now a growing awareness of the need to extend the research focus to systems with more general patterns of energy injection and dissipation. These include various types of complex fluids and plasmas, as well as active systems consisting of self-propelled particles, like dense bacterial suspensions. Recently, a continuum model has been proposed for such “living fluids” that is based on the Navier–Stokes equations, but extends them to include some of the most general terms admitted by the symmetry of the problem [Wensink HH, et al. (2012) Proc Natl Acad Sci USA 109:14308–14313]. This introduces a cubic nonlinearity, related to the Toner–Tu theory of flocking, which can interact with the quadratic Navier–Stokes nonlinearity. We show that as a result of the subtle interaction between these two terms, the energy spectra at large spatial scales exhibit power laws that are not universal, but depend on both finite-size effects and physical parameters. Our combined numerical and analytical analysis reveals the origin of this effect and even provides a way to understand it quantitatively. Turbulence in active fluids, characterized by this kind of nonlinear self-organization, defines a new class of turbulent flows.

Effect of Particle Finite Size on Gas Turbulent Flow

2012 ◽  
Vol 516-517 ◽  
pp. 752-757
Author(s):  
Zhuo Xiong Zeng ◽  
Zhang Jun Wang ◽  
Yun Ni Yu
Keyword(s):  
Turbulent Flows ◽  
Finite Size ◽  
Turbulence Energy ◽  
Particle Sizes ◽  
Wake Effect ◽  
Moving Wall ◽  
Restricted Region ◽  
Left And Right ◽  
Freely Moving ◽  
Moving Particle

Dynamic mesh and moving wall technique were employed to simulate the unsteady flow field of moving particle with finite size. For freely moving particle, it does not come into being particle wake. Middle particle can move straightforward outlet, but left and right particles move disorderly in a restricted region. Vortex location varies with the change of particle location. Turbulence energy and pressure is decreased gradually from inlet to outlet. But for moving particle with slip velocity between gas and particle, particle wake comes into being. Turbulence enhancement by particle wake effect is studied by numerical simulation of gas turbulent flows passing over particle under various particle sizes, inlet gas velocities, gas viscosity, gas density and the distance of particles.

Study of Local Turbulence Profiles Relative to the Particle Surface in Particle-Laden Turbulent Flows

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Lian-Ping Wang ◽  
Oscar G. C. Ardila ◽  
Orlando Ayala ◽  
Hui Gao ◽  
Cheng Peng
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flows ◽  
Isotropic Turbulence ◽  
Model Development ◽  
Particle Surface ◽  
Finite Size ◽  
Solid Particles ◽  
Energy Profiles ◽  
Turbulence Transport ◽  
Boltzmann Method

As particle-resolved simulations (PRSs) of turbulent flows laden with finite-size solid particles become feasible, methods are needed to analyze the simulated flows in order to convert the simulation data to a form useful for model development. In this paper, the focus is on turbulence statistics at the moving fluid–solid interfaces. An averaged governing equation is developed to quantify the radial transport of turbulent kinetic energy when viewed in a frame moving with a solid particle. Using an interface-resolved flow field solved by the lattice Boltzmann method (LBM), we computed each term in the transport equation for a forced, particle-laden, homogeneous isotropic turbulence. The results illustrate the distributions and relative importance of volumetric source and sink terms, as well as pressure work, viscous stress work, and turbulence transport. In a decaying particle-laden flow, the dissipation rate and kinetic energy profiles are found to be self-similar.

Improved DRW Model for Prediction of Deposition and Dispersion of Nano- and Micro-Particles in Turbulent Flows

2020 ◽  
Author(s):  
Amir A. Mofakham ◽  
Goodarz Ahmadi
Keyword(s):  
Turbulent Flows ◽  
Time Scale ◽  
Correction Term ◽  
Particle Dispersion ◽  
Nano Particles ◽  
Concentration Profiles ◽  
Drift Correction ◽  
Velocity Fluctuations ◽  
Fluctuation Velocity ◽  
Point Particles

Abstract In this study, the accuracy of the discrete random walk (DRW) stochastic model in generating the instantaneous velocity fluctuations as seen by micro- and nano-particles in inhomogeneous turbulent flows were examined. Particular attention was given to the effects of the non-uniform normal RMS velocity fluctuations and turbulence time scale on the DRW model predictions. The trajectories of randomly injected point-particles with diameters ranging from 10 nm to 30 μm in a duct were evaluated using an in-house Matlab particle tracking code. The particle equation of motion included the drag and Brownian forces. The fully developed mean velocity and RMS fluctuation velocity profiles were exported from the RANS (v2f) simulations and were used for the particle dispersion and transport analysis. It was assumed that the particle-laden flow is sufficiently dilute so that the particle-particle collisions and the two-way coupling effects of particles on the flow could be ignored. To incorporate the instantaneous turbulence velocity fluctuations effects on particle dispersion, the Conventional-DRW model (in the absence of drift corrections), which was originally developed for homogenous turbulent flows, was first used. It was shown that the Conventional-DRW model leads to superfluous migration of fluid-point particles toward the wall and erroneous particle deposition rate. The Modified-DRW model with an appropriate velocity gradient drift correction term was also tested. It was found that the predicted concentration profiles of tracer particles still are not uniform. It was hypothesized that the reason for this erroneous prediction is due to the inhomogeneous turbulence time macroscale in the channel flow. A new drift correction term as a function of gradients of both RMS fluctuation velocity and the turbulence time macroscale was proposed. It was shown that the new Improved-DRW model with the velocity and time scale drift corrections leads to uniform distributions for fluid-point particles and reasonable concentration profiles for finite-size particles. It was shown that the predicted deposition velocities of different size particles by the proposed Improved-DRW model are in good agreement with the available experimental data as well as the predictions of the empirical models and earlier DNS results.

Sign in / Sign up

Export Citation Format

Share Document