Effect of Particle-Particle Collisions on the Spatial Distribution of Inertial Particles Suspended in Homogeneous Isotropic Turbulent Flows

AbstractThree physical mechanisms which may affect dispersion of particle’s motion in wall-bounded turbulent flows, including the effects of turbulence, wall roughness in particle-wall collisions, and inter-particle collisions, are numerically investigated in this study. Parametric studies with different wall roughness extents and with different mass loading ratios of particles are performed in fully developed channel flows with the Eulerian-Lagrangian approach. A low-Reynolds-numberk–εturbulence model is applied for the solution of the carrier-flow field, while the deterministic Lagrangian method together with binary-collision hard-sphere model is applied for the solution of particle motion. It is shown that the mechanism of inter-particle collisions should be taken into account in the modeling except for the flows laden with sufficiently low mass loading ratios of particles. Influences of wall roughness on particle dispersion due to particle-wall collisions are found to be considerable in the bounded particle–laden flow. Since the investigated particles are associated with large Stokes numbers, i.e., larger thanO(1), in the test problem, the effects of turbulence on particle dispersion are much less considerable, as expected, in comparison with another two physical mechanisms investigated in the study.

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Velocity and spatial distribution of inertial particles in a turbulent channel flow

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.355 ◽

2019 ◽

Vol 872 ◽

pp. 367-406 ◽

Cited By ~ 9

Author(s):

Kee Onn Fong ◽

Omid Amili ◽

Filippo Coletti

Keyword(s):

Spatial Distribution ◽

Particle Velocity ◽

Turbulent Channel Flow ◽

Wall Turbulence ◽

Buffer Layers ◽

Working Fluid ◽

Wall Region ◽

Inertial Particles ◽

Velocity Fluctuations ◽

Near Wall

We present experimental observations of the velocity and spatial distribution of inertial particles dispersed in turbulent downward flow through a vertical channel at friction Reynolds numbers $\mathit{Re}_{\unicode[STIX]{x1D70F}}=235$ and 335. The working fluid is air laden with size-selected glass microspheres, having Stokes numbers $St=\mathit{O}(10)$ and $\mathit{O}(100)$ when based on the Kolmogorov and viscous time scales, respectively. Cases at solid volume fractions $\unicode[STIX]{x1D719}_{v}=3\times 10^{-6}$ and $5\times 10^{-5}$ are considered. In the more dilute regime, the particle concentration profile shows near-wall and centreline maxima compatible with a turbophoretic drift down the gradient of turbulence intensity; the particles travel at speed similar to that of the unladen flow except in the near-wall region; and their velocity fluctuations generally follow the unladen flow level over the channel core, exceeding it in the near-wall region. The denser regime presents substantial differences in all measured statistics: the near-wall concentration peak is much more pronounced, while the centreline maximum is absent; the mean particle velocity decreases over the logarithmic and buffer layers; and particle velocity fluctuations and deposition velocities are enhanced. An analysis of the spatial distributions of particle positions and velocities reveals different behaviours in the core and near-wall regions. In the channel core, dense clusters form which are somewhat elongated, tend to be preferentially aligned with the vertical/streamwise direction and travel faster than the less concentrated particles. In the near-wall region, the particles arrange in highly elongated streaks associated with negative streamwise velocity fluctuations, several channel heights in length and spaced by $\mathit{O}(100)$ wall units, supporting the view that these are coupled to fluid low-speed streaks typical of wall turbulence. The particle velocity fields contain a significant component of random uncorrelated motion, more prominent for higher $St$ and in the near-wall region.

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Heavy inertial particles in turbulent flows gain energy slowly but lose it rapidly

Physical Review E ◽

10.1103/physreve.97.033102 ◽

2018 ◽

Vol 97 (3) ◽

Cited By ~ 5

Author(s):

Akshay Bhatnagar ◽

Anupam Gupta ◽

Dhrubaditya Mitra ◽

Rahul Pandit

Keyword(s):

Turbulent Flows ◽

Inertial Particles ◽

Gain Energy

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Direct Numerical Simulation of Gas-Particle Turbulent Swirling Flows in an Axially Rotating Pipe

Volume 1: Fora, Parts A, B, C, and D ◽

10.1115/fedsm2003-45186 ◽

2003 ◽

Cited By ~ 1

Author(s):

Kazuyoshi Matsuzaki ◽

Mizue Munekata ◽

Hideki Ohba

Keyword(s):

Numerical Simulation ◽

Direct Numerical Simulation ◽

Turbulent Flows ◽

Particle Concentration ◽

Fluid Motion ◽

Swirling Flows ◽

Particle Collisions ◽

Pipe Radius ◽

The One ◽

Very High

The purpose of this study is to investigate the effect of the turbulent structure of the swirling flows on the particle motions using numerical simulation. In this work, we deal with the swirling turbulent flows in an axially rotating pipe because of focusing on the influence of swirl effect on the particle motions. Direct numerical simulation (DNS) of gas-particle turbulent swirling flows in the axially rotating pipe at the Reynolds number 180, based on the friction velocity and the pipe radius, and the rotating ratios 0.25 and 0.3 based on the bulk velocity was performed. Particle motions were treated by a Lagragian method with inter-particle collisions calculated by a deterministic method. In order to investigate the influence of swirl effect on the particle motions in detail, the one-way method in which fluid motion is not affected by particles is adopted. In particular, the effect of the inter-particle collisions on particle motions was carefully investigated because it is considered that particles accumulate near the wall due to the centrifugal force and local particle concentration is very high in the region.

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Effects of forcing time scale on the simulated turbulent flows and turbulent collision statistics of inertial particles

Physics of Fluids ◽

10.1063/1.4906334 ◽

2015 ◽

Vol 27 (1) ◽

pp. 015105 ◽

Cited By ~ 6

Author(s):

B. Rosa ◽

H. Parishani ◽

O. Ayala ◽

L.-P. Wang

Keyword(s):

Turbulent Flows ◽

Time Scale ◽

Inertial Particles

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Wall accumulation and spatial localization in particle-laden wall flows

Journal of Fluid Mechanics ◽

10.1017/jfm.2012.65 ◽

2012 ◽

Vol 699 ◽

pp. 50-78 ◽

Cited By ~ 83

Author(s):

G. Sardina ◽

P. Schlatter ◽

L. Brandt ◽

F. Picano ◽

C. M. Casciola

Keyword(s):

Turbulent Flows ◽

Pair Correlation ◽

Turbulent Channel Flow ◽

Wall Turbulence ◽

Small Scale ◽

Wall Region ◽

Inertial Particles ◽

Wall Flows ◽

Domain Truncation ◽

Near Wall

AbstractWe study the two main phenomenologies associated with the transport of inertial particles in turbulent flows, turbophoresis and small-scale clustering. Turbophoresis describes the turbulence-induced wall accumulation of particles dispersed in wall turbulence, while small-scale clustering is a form of local segregation that affects the particle distribution in the presence of fine-scale turbulence. Despite the fact that the two aspects are usually addressed separately, this paper shows that they occur simultaneously in wall-bounded flows, where they represent different aspects of the same process. We study these phenomena by post-processing data from a direct numerical simulation of turbulent channel flow with different populations of inertial particles. It is shown that artificial domain truncation can easily alter the mean particle concentration profile, unless the domain is large enough to exclude possible correlation of the turbulence and the near-wall particle aggregates. The data show a strong link between accumulation level and clustering intensity in the near-wall region. At statistical steady state, most accumulating particles aggregate in strongly directional and almost filamentary structures, as found by considering suitable two-point observables able to extract clustering intensity and anisotropy. The analysis provides quantitative indications of the wall-segregation process as a function of the particle inertia. It is shown that, although the most wall-accumulating particles are too heavy to segregate in homogeneous turbulence, they exhibit the most intense local small-scale clustering near the wall as measured by the singularity exponent of the particle pair correlation function.

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