Collision efficiency of non-Brownian spheres in a simple shear flow – the role of non-continuum hydrodynamic interactions

Patra, Pijush; Koch, Donald L.; Roy, Anubhab

doi:10.1017/jfm.2022.817

Cited by 5 publications

(1 citation statement)

References 41 publications

(96 reference statements)

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“…The Knudsen number , where is the mean free path of the medium and is the average of the sphere radii and , measures the strength of non-continuum effects. Previous studies have obtained collision rates due to non-continuum interactions for particles subject to differential sedimentation, uniaxial compressional flow (Dhanasekaran, Roy & Koch 2021 a ), simple shear flow (Patra, Koch & Roy 2022), Brownian motion (Patra & Roy 2022) and turbulent flow (Dhanasekaran, Roy & Koch 2021 b ). Surface deformations of droplet pairs in Stokes flow become significant when the lubrication pressure becomes comparable to the Laplace pressure.…”

Section: Introductionmentioning

confidence: 99%

Collision efficiency of like-charged spheres settling in a quiescent environment

2023

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We study the gravity-induced collisions of charged spheres of dielectric materials dispersed in a gaseous medium. When the gap thickness between the surfaces of two spheres is shorter than the mean free path of the surrounding fluid medium, continuum assumptions for the hydrodynamics interactions are no longer valid, and the non-continuum lubrication interactions result in surface-to-surface contact in finite time. Two like-charged dielectric spheres attract each other at close separations for a wide range of size and charge ratio values. We use trajectory analysis to calculate the collision rate and, thus, explore the role of electrostatic interactions in the collision dynamics of a pair of like-charged dielectric spheres. We present the modifications of pair trajectories due to electrostatic forces and show how collision efficiencies vary with the non-dimensional parameter capturing the relative strength of the electrostatic force to gravity as well as the charge ratio and size ratio.

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Section: Introductionmentioning

confidence: 99%

Collision efficiency of like-charged spheres settling in a quiescent environment

2023

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Collision Statistics of Droplets in Turbulence Considering Lubrication Interactions, Mobility of Interfaces, and Non-continuum Molecular Effects

Ababaei

Michel

Rosa

2023

Flow Turbulence Combust

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Collision statistics of same-size aerodynamically interacting droplets in homogeneous isotropic turbulence is examined via hybrid direct numerical simulations combined with Lagrangian particle tracking under a point-particle assumption and a one-way momentum coupling. The simulations are performed both in the absence and presence of gravity for various droplet Stokes numbers (0.1–2) over a wide range of liquid water contents (LWCs = 1–30 $$\text {g/m}^3$$ g/m 3 ). Also, the effects of using different representations of the lubrication forces, i.e. a continuum and a non-continuum one, have been investigated. The results have highlighted the importance of considering the aerodynamic interaction, especially in the presence of gravity for the systems that have high LWCs. Likewise, taking the lubrication force into account shows a notable change in statistics, but a non-continuum representation yields results that are close to the continuum one. In addition, the impact of modeling droplets as fluid drops instead of rigid particles has been examined. Obtaining quite close statistics under both cases demonstrates that a rigid particle assumption for water droplets in air is sufficiently accurate owing to the high water-to-air viscosity ratio. Moreover, the collision efficiency is shown to be in the range 60–100% in the absence of gravity, which approaches 100% as the LWC is enlarged. In the presence of gravity, however, the efficiency grows, with both the Stokes number and the LWC, to values as high as 300%. Finally, for settling droplet systems, the enhancement factor due to turbulence is quantified, exhibiting a growth with the LWC and a reduction with the Stokes number.

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Instability of a dusty shear flow

Nath,

Roy,

Kasbaoui

2024

J. Fluid Mech.

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We study the instability of a dusty simple shear flow where the dust particles are distributed non-uniformly. A simple shear flow is modally stable to infinitesimal perturbations. Also, a band of particles remains unaffected in the absence of any background flow. However, we demonstrate that the combined scenario – comprising a simple shear flow with a localized band of particles – can exhibit destabilization due to their two-way interaction. The instability originates solely from the momentum feedback from the particle phase to the fluid phase. Eulerian–Lagrangian simulations are employed to illustrate the existence of this instability. Furthermore, the results are compared with a linear stability analysis of the system using an Eulerian–Eulerian model. Our findings indicate that the instability has an inviscid origin and is characterized by a critical wavelength below which it is not persistent. We have observed that increasing particle inertia dampens the unstable modes, whereas the strength of the instability increases with the strength of the coupling between the fluid and particle phases.

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Collision efficiency of non-Brownian spheres in a simple shear flow – the role of non-continuum hydrodynamic interactions

Cited by 5 publications

References 41 publications

Collision efficiency of like-charged spheres settling in a quiescent environment

Collision efficiency of like-charged spheres settling in a quiescent environment

Collision Statistics of Droplets in Turbulence Considering Lubrication Interactions, Mobility of Interfaces, and Non-continuum Molecular Effects

Instability of a dusty shear flow

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