Effects of finite-size heavy particles on the turbulent flows in a square duct

Lin, Zhaowu; Shao, Xueming; Yu, Zhaosheng; Wang, Lian‐Ping

doi:10.1016/s1001-6058(16)60737-0

Cited by 26 publications

(11 citation statements)

References 16 publications

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“…Nevertheless, for the case of heavy particles, the relative difference between the bulk velocities from two collision models can reach a few percent when most particles settle down to the bottom wall. 32…”

Section: B Mean Streamwise Velocitymentioning

confidence: 99%

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Effects of finite-size neutrally buoyant particles on the turbulent flows in a square duct

Lin

Shao

et al. 2017

Physics of Fluids

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Interface-resolved direct numerical simulations of the particle-laden turbulent flows in a square duct are performed with a direct-forcing fictitious domain method. The effects of the finite-size particles on the mean and root-mean-square (RMS) velocities are investigated at the friction Reynolds number of 150 (based on the friction velocity and half duct width) and the particle volume fractions ranging from 0.78% to 7.07%. Our results show that the mean secondary flow is enhanced and its circulation center shifts closer to the center of the duct cross section when the particles are added. The reason for the particle effect on the mean secondary flow is analyzed by examining the terms in the mean streamwise vorticity equation. It is observed that the particles enhance the gradients of the secondary Reynolds normal stress difference and shear stress in the near-wall region near the corners, which we think is mainly responsible for the enhancement in the mean secondary flow. Under a prescribed driving pressure gradient, the presence of particles attenuates the bulk velocity and the turbulent intensity. All particle-induced effects are intensified with increasing particle volume fraction and decreasing particle size, if other parameters are fixed. In addition, the particles accumulate preferentially in the near-corner region. The effects of the type of the collision model (i.e., if friction and damping are included or not) on the results are found significant, but not so significant to bring about qualitatively different results.

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Section: B Mean Streamwise Velocitymentioning

confidence: 99%

“…We note that a companion paper on the effects of the heavy particles on the turbulent duct flow has recently been published during the revision of the present work. 32 The paper is organized as follows. In Sec.…”

Section: Introductionmentioning

confidence: 99%

Effects of finite-size neutrally buoyant particles on the turbulent flows in a square duct

Lin

Shao

et al. 2017

Physics of Fluids

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“…The latter is thought to be maximized when the particle response time, τ p , is comparable to the Kolmogorov time scale, τ η , such that the Stokes number St η = τ p /τ η is of order unity (Wang & Maxey 1993, Fessler et al misestimate significant aspects (Balachandar & Eaton 2010). The availability of everincreasing computational capabilities has allowed particle-resolved DNS to investigate relatively large numbers of particles in wall-bounded turbulent flows without the need of modeling the momentum exchange (Garcia-Villalba et al 2012;Picano et al 2015;Lin et al 2017;Wang et al 2017). Those studies, however, can typically deal with O(10 4 ) particles much larger than the viscous scales, as opposed to the millions of sub-Kolmogorov particles usually present in point-particle simulations.…”

Section: Introductionmentioning

confidence: 99%

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

2019

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We present experimental observations of the velocity and spatial distribution of inertial particles dispersed in the turbulent downward flow through a vertical channel at friction Reynolds numbers Re τ = 235 and 335. The working fluid is air laden with size-selected glass micro-spheres, having Stokes numbers St = O(10) and O(100) when based on the Kolmogorov and viscous time scales, respectively. Cases at solid volume fractions φ v = 3×10 −6 and 5×10 −5 are considered. In the more dilute regime, the particle concentration profile shows near-wall and centerline maxima compatible with a turbophoretic drift down the gradient of turbulence intensity; the particles travel at similar speed as 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 centerline 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 behaviors 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 to negative streamwise velocity fluctuations, several channel height in length and spaced by 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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“…The effects of solid-to-fluid density ratio ρ p /ρ f , mass fraction, polidispersity and shape have also been studied by Fornari et al (2016bFornari et al ( , 2018; Lashgari et al (2017b); Ardekani et al (2017). Recently, Lin et al (2017) used a direct-forcing fictitious method to study turbulent duct flows laden with a dilute suspension of finite-size spheres heavier than the carrier fluid. Spheres with radius a = h/10 (with h the duct half-width) were considered at a solid volume fraction φ = 2.36%.…”

Section: Introductionmentioning

confidence: 99%

Suspensions of finite-size neutrally buoyant spheres in turbulent duct flow

et al. 2018

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We study the turbulent square duct flow of dense suspensions of neutrally-buoyant spherical particles. Direct numerical simulations (DNS) are performed in the range of volume fractions φ = 0−0.2, using the immersed boundary method (IBM) to account for the dispersed phase. Based on the hydraulic diameter a Reynolds number of 5600 is considered. We report flow features and particle statistics specific to this geometry, and compare the results to the case of two-dimensional channel flows. In particular, we observe that for φ = 0.05 and 0.1, particles preferentially accumulate on the corner bisectors, close to the duct corners as also observed for laminar square duct flows of same duct-to-particle size ratios. At the highest volume fraction, particles preferentially accumulate in the core region. For channel flows, in the absence of lateral confinement particles are found instead to be uniformily distributed across the channel. We also observe that the intensity of the cross-stream secondary flows increases (with respect to the unladen case) with the volume fraction up to φ = 0.1, as a consequence of the high concentration of particles along the corner bisector. For φ = 0.2 the turbulence activity is strongly reduced and the intensity of the secondary flows reduces below that of the unladen case. The friction Reynolds number increases with φ in dilute conditions, as observed for channel flows. However, for φ = 0.2 the mean friction Reynolds number decreases below the value for φ = 0.1.

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Effects of finite-size heavy particles on the turbulent flows in a square duct

Cited by 26 publications

References 16 publications

Effects of finite-size neutrally buoyant particles on the turbulent flows in a square duct

Effects of finite-size neutrally buoyant particles on the turbulent flows in a square duct

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

Suspensions of finite-size neutrally buoyant spheres in turbulent duct flow

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