Alignment statistics of rods with the Lagrangian stretching direction in a channel flow

Cui, Zhiwen; Dubey, Anshuman; Zhao, Lihao; Mehlig, B.

doi:10.1017/jfm.2020.547

Cited by 16 publications

(6 citation statements)

References 55 publications

(118 reference statements)

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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%

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

confidence: 99%

“…2019 b ; Cui et al. 2020 b , 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.…”

Section: Introductionmentioning

confidence: 99%

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.

Self Cite

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“…Numerical investigations have greatly helped to understand the effect of shape on the dynamics, orientation and alignment of anisotropic particles in turbulence. Many works have been focused on homogeneous and isotropic turbulence (HIT), but important works also investigated the influence of non-homogeneity on the particles dynamics in the presence of more complex flows, such as wall-bounded flows (Marchioli, Fantoni & Soldati 2010;Zhao et al 2015;Zhao & Andersson 2016;Cui et al 2020). Experiments have contributed to a detailed understanding of the dynamics of anisotropic particles, with most of the works in the HIT configuration (Parsa et al 2012;Parsa & Voth 2014;Pujara et al 2018) and only few in turbulent channel flow.…”

Section: Introductionmentioning

confidence: 99%

Influence of Reynolds number on the dynamics of rigid, slender and non-axisymmetric fibres in channel flow turbulence

2022

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We investigate experimentally the dynamics of non-axisymmetric fibres in channel flow turbulence, focusing specifically on the importance of the fibre size relative to the flow scales. To this aim, we maintain the same physical size of the fibres and we increase the shear Reynolds number. Experiments are performed in the TU Wien Turbulent Water Channel for three values of shear Reynolds number, namely 180, 360 and 720. Fibres are slender – length to diameter ratio of 120 – rigid, curved and neutrally buoyant particles and their shape ranges from low curvature – almost straight fibres – to moderate curvature. In all cases, fibre size remains small compared with the channel height (${\leqslant }1.5\,\%$). Three-dimensional and time-resolved recordings of the laser-illuminated measurement region are obtained from four high-speed cameras and used to infer fibre dynamics. With the aid of multiplicative algebraic reconstruction techniques, fibre position, orientation, velocity and rotation rates are determined. Our measurements span over the half-channel height, from wall to centre, and allow a complete characterisation of the fibre dynamics in all regions of the flow. Specifically, we measure fibre preferential distribution and orientation. We observe that the fibre dynamics is always influenced by their curvature. Through a comparison between measurements of the near-wall dynamics of the fibres and the near-wall dynamics of the flow, we identify a causal relationship between fibre velocity and orientation, and the near-wall turbulence dynamics. Finally, we have been able to provide original measurements of the tumbling rate of the fibres, for which we report the influence of fibre curvature. We underline that our measurements confirm previous findings obtained in numerical and experimental works.

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“…In an Eulerian approach, the alignment with the eigenvectors of the strain rate and the fluid velocity has been studied 18,19,24 . It has been found that a simpler picture emerges if one describes the local alignment in the reference formed in the Lagrangian framework [25][26][27] . The physical image of the Lagrangian reference frame is suggested as below.…”

Section: Introductionmentioning

confidence: 99%

Accumulation and alignment of elongated gyrotactic swimmers in turbulence

Liu,

Jiang,

Sun

2022

Preprint

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We study the dynamics of gyrotactic swimmers in turbulence, whose orientation is governed by gravitational torque and local fluid velocity gradient. The gyrotaxis strength is measured by the ratio of the Kolmogorov time scale to the reorientation time scale due to gravity, and a large value of this ratio means the gyrotaxis is strong. By means of direct numerical simulations, we investigate the effects of swimming velocity and gyrotactic stability on spatial accumulation and alignment. Three-dimensional Voronoï analysis is used to study the spatial distribution and time evolution of the particle concentration. We study spatial distribution by examing the overall preferential sampling and where clusters and voids (subsets of particles that have small and large Voronoï volumes respectively) form. Compared with the ensemble particles, the preferential sampling of clusters and voids is found to be more pronounced. The clustering of fast swimmers lasts much longer than slower swimmers when the gyrotaxis is strong and intermediate, but an opposite trend emerges when the gyrotaxis is weak. In addition, we study the preferential alignment with the Lagrangian stretching direction, with which passive slender rods have been known to align. We show that the Lagrangian alignment is reduced by the swimming velocity when the gyrotaxis is weak, while the Lagrangian alignment is enhanced for the regime in which gyrotaxis is strong.

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Alignment statistics of rods with the Lagrangian stretching direction in a channel flow

Abstract: Abstract

Cited by 16 publications

References 55 publications

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

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

Influence of Reynolds number on the dynamics of rigid, slender and non-axisymmetric fibres in channel flow turbulence

Accumulation and alignment of elongated gyrotactic swimmers in turbulence

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