Alignment of slender fibers and thin disks induced by coherent structures of wall turbulence

Cui, Zhiwen; Huang, Wei‐Xi; Xu, Chunxiao; Andersson, Helge I.; Zhao, Lihao

doi:10.1016/j.ijmultiphaseflow.2021.103837

Cited by 12 publications

(5 citation statements)

References 52 publications

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“…where u(x, t) and p(x, t) are the velocity and pressure fields, ρ is the fluid density, τ is the stress tensor, and f fib is the feedback forcing from the fibre. Here, f turb is the external forcing term used to sustain turbulence, chosen to be the Arnold-Beltrami-Childress forcing (Dombre et al 1986) given by…”

Section: Methodsmentioning

confidence: 99%

“…This property is also highly dependent on the configuration: e.g. in homogeneous isotropic turbulence flows, fibres are known to usually align with the intermediate eigenvector of the strain rate tensor, whereas for channels, they are a function of the channel height, largely influenced by the coherent structures (Cui et al 2021). Clearly, the alignment can also be influenced by viscoelastic stresses; experiments with low Reynolds number simple shear flows have shown that orientation of semi-dilute fibre suspensions in weakly (Iso, Koch & Cohen 1996b) and highly (Iso et al 1996a) elastic fluids change in comparison to their aligned directions in Newtonian flows (Stover, Koch & Cohen 1992).…”

Section: Alignmentmentioning

confidence: 99%

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The dynamics of fibres dispersed in viscoelastic turbulent flows

Aswathy,

Rosti

2024

J. Fluid Mech.

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This study explores the dynamics of finite-size fibres suspended freely in a viscoelastic turbulent flow. For a fibre suspended in Newtonian flows, two different flapping regimes were identified by Rosti et al. (Phys. Rev. Lett., vol. 121, issue 4, 2018, 044501): one dominated by time scales from the flow, and another dominated by time scales associated with its natural frequency. We explore in this work how the fibre dynamics is modified by the elasticity of the carrier fluid. For this, we perform direct numerical simulations of a two-way coupled fibre–fluid system in a parametric space spanning different Deborah numbers, fibre bending stiffness (flexible to rigid) and linear density difference between the fibre and the flow (neutrally buoyant to denser-than-fluid fibres). We examine how these parameters influence various fibre characteristics such as the frequency of flapping, curvature, and alignment with the fluid strain and polymer stretching directions. Results reveal that the neutrally buoyant fibres, depending on their flexibility, oscillate with large and small time scales transpiring from the flow, but the smaller time scales are suppressed as the polymer elasticity increases. Polymer stretching is uncommunicative to denser-than-fluid fibres, which flap with large time scales from the flow when flexible, and with their natural frequency when rigid. Thus the characteristic elastic time scale has a subdominant effect when the fibres are neutrally buoyant, while its effect is absent when the fibres become more inertial. In addition, we also explore the fibre's bending curvature and its preferential alignment with the flow to identify the other roles of viscoelasticity in modifying the coupled fluid–structure dynamics. Inertial fibres have larger curvatures and are less responsive to the polymer presence, whereas the neutrally buoyant fibres show quantitative changes. The perceptible passivity of the denser fibres is again reflected in the way they align preferentially with the polymeric stretching directions: the neutrally buoyant fibres show a higher alignment with the polymer stretching directions compared to the denser ones. In a nutshell, the polymers exert a larger influence on neutrally buoyant fibres, which are more reflective of the polymeric influence in the flow. The study addresses comprehensively the interplay between polymer elasticity and the fibre structural properties in determining its response behaviour in an elasto-inertial turbulent flow.

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Section: Methodsmentioning

confidence: 99%

Section: Alignmentmentioning

confidence: 99%

The dynamics of fibres dispersed in viscoelastic turbulent flows

Aswathy,

Rosti

2024

J. Fluid Mech.

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“…For Re p 1, the models include the Stokes resistance (Brenner 1963(Brenner , 1964Brenner & Cox 1963) and Jeffery torque (Jeffery 1922) for non-spherical particles. In the PP-DNSs without considering the effect of gravity, the weak inertial or inertialess prolate spheroids near the wall tend to align their symmetry axes with the streamwise direction, while the weak inertial or inertialess oblate spheroids preferentially align their symmetry axes with the wall-normal direction (Marchioli et al 2010;Challabotla, Zhao & Andersson 2015b;Zhao et al 2015;Jie et al 2019b;Cui et al 2020bCui et al , 2021. As the particle inertia increases, prolate spheroids have a tendency to tumble, while oblate spheroids preferentially spin in the streamwise-wall-normal plane near the wall (Marchioli et al 2010;Marchioli & Soldati 2013;Challabotla et al 2015a;Zhao et al 2015Zhao et al , 2019.…”

Section: Angular Dynamics Of Spheroidal Particles In Turbulent Channe...mentioning

confidence: 99%

“…Note that only the wall-normal particle velocity is reversed and the particle orientation remains the same after a collision. The same computational method has been widely employed in our previous studies (Challabotla et al 2015a;Cui et al 2020bCui et al , 2021Jie et al 2022). In this study, we tracked swarms of 300 000 spheroids of each case with the aspect ratio ranging from 0.02 to 50, and Stokes number ranging from 1 to 100.…”

Section: Direct Numerical Simulations Of Fluid and Particlesmentioning

confidence: 99%

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Effect of fluid inertial torque on the rotational and orientational dynamics of tiny spheroidal particles in turbulent channel flow

Cui,

Qiu,

Jiang

et al. 2023

J. Fluid Mech.

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Rotation and orientation of non-spherical particles in a fluid flow depend on the hydrodynamic torque they experience. However, little is known about the effect of the fluid inertial torque on the dynamics of tiny inertial spheroids in turbulent channel flows, as only Jeffery torque has been considered in previous studies by point-particle direct numerical simulations. In this study, we investigate the rotation and orientation of tiny spheroids with both fluid inertial torque and Jeffery torque in a turbulent channel flow. By comparing with the case in the absence of fluid inertial torque, we find that the rotational and orientational dynamics of spheroids is significantly affected by the fluid inertial torque when the Stokes number, which is non-dimensionalized by fluid viscous time scale, is larger than the critical value $St_c\approx 2$ , indicating that the fluid inertial torque is non-negligible for most particle cases considered in earlier studies. In contrast to the earlier findings considering only Jeffery torque (Challabotla et al., J. Fluid Mech., vol. 776, 2015, p. R2), we find that prolate (oblate) spheroids with a large Stokes number tend to tumble (spin) in the streamwise–wall-normal plane in a thinner region near the wall due to the presence of the fluid inertial torque. Approaching the channel centre, the flow shear gradually vanishes, but the velocity difference between local fluid and particles is still pronounced and increasing as particle inertia grows. As a result, in the core region, fluid inertial torque is dominant and drives the particles to align with its broad side normal to the streamwise direction rather than a random orientation observed in earlier studies without fluid inertial torque. Meanwhile, the presence of fluid inertial torque enhances the tumbling rates of spheroids in the core region. In addition, the effect of fluid inertial force on the dynamics of spheroids is also examined in this study, but the results indicate the effect of fluid inertial force is weak. Our findings imply the importance of fluid inertial torque in modelling the dynamics of inertial non-spherical particles in turbulent channel flows.

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槽道湍流中无惯性椭球颗粒在结构主导区域的取向行为: 形状影响

Cui,

Zhao

2024

Acta Mech. Sin.

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Alignment of slender fibers and thin disks induced by coherent structures of wall turbulence

Cited by 12 publications

References 52 publications

The dynamics of fibres dispersed in viscoelastic turbulent flows

The dynamics of fibres dispersed in viscoelastic turbulent flows

Effect of fluid inertial torque on the rotational and orientational dynamics of tiny spheroidal particles in turbulent channel flow

槽道湍流中无惯性椭球颗粒在结构主导区域的取向行为: 形状影响

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