Long non-axisymmetric fibres in turbulent channel flow

Alipour, Mobin; Paoli, Marco De; Ghaemi, Sina; Soldati, Alfredo

doi:10.1017/jfm.2021.185

Cited by 16 publications

(10 citation statements)

References 81 publications

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“…It descends that the action exerted by the fibers onto the flow is primarily associated with the rotational dynamic of the fibers, rather than translational motion. In fact, this latter motion is mostly in the horizontal, stream-wise direction, as shown by several authors ( [14,19] among others). In Figure 8, the same quantities are shown in the case of high particle concentration.…”

Section: Carrier Flowmentioning

confidence: 52%

“…In the validation step, spurious vectors are dropped according to a local median test carried out on a 9-point square kernel. Table 1 summarizes the main parameters of the current experimental setup compared to reference data from [19,34]. Respectively U 0 , u τ , Re H , Re τ represent the mean centerline channel velocity, the friction velocity, the Reynolds number based on the centerline velocity Re H = U 0 H/ν, and the friction Reynolds number Re τ = u τ H/ν, where ν is the kinematic viscosity of water at 20 • C. [34] 0.13 0.00684 5540 290…”

Section: Carrier Flow Velocity Field Measurementmentioning

confidence: 99%

“…Furthermore, the volume fraction of the multiphase suspension does not appear to affect the way dispersed particles accumulate within the channel. Cosine of average in-plane angle of fibers |cos ϕ| is presented in Figure 11, compared to experimental data from [19], with elongated particles with an aspect ratio of 30.7. Close to the wall, fiber particles tend to align on average to the main flow direction, whereas as they depart from the near-wall region, they tend take on the centerline orientation.…”

Section: Dispersed Particlesmentioning

confidence: 99%

“…Several authors focused on fiber particles behavior in a range of turbulent flow configurations by experiments and simulations [13][14][15][16]. Recent works have investigated specific aspects such as the rotational dynamics of elongated particles and the behavior of non-axisymmetric particles in channel flow [17][18][19]. The role of fiber length on the fiber dynamics in a turbulent channel flow was investigated experimentally by [20].…”

Section: Introductionmentioning

confidence: 99%

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Flow-Particle Coupling in a Channel Flow Laden with Elongated Particles: The Role of Aspect Ratio

Capone

Felice

Pereira

2021

JMSE

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A turbulent channel flow laden with elongated, fiber-like particles is investigated experimentally by optical techniques. The flow-particle inter-coupling is analyzed in the case of particles with an aspect ratio of 40 and 80, at two volume fractions, 10−5 and 10−4. An image processing technique is presented, which is employed to simultaneously obtain carrier flow velocimetry data and distribution and orientation data of dispersed particles. Turbulence enhancement is reported in the near-wall region, with a higher level of increase associated with higher aspect ratio particles. Comparison to fiber data suggests that this mechanism of turbulence modulation stems from a particles orientational behavior. The preferential particle distribution is reported to be dependent on the aspect ratio in the region close to the wall. The probability density function of the fibers’ orientation angle appears to be independent of the particle aspect ratio once it is conditioned to the fibers’ characteristic size.

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Section: Carrier Flowmentioning

confidence: 52%

Section: Carrier Flow Velocity Field Measurementmentioning

confidence: 99%

Section: Dispersed Particlesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Flow-Particle Coupling in a Channel Flow Laden with Elongated Particles: The Role of Aspect Ratio

Capone

Felice

Pereira

2021

JMSE

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“…Recently, Alipour et al. (2021) investigated curved fibres in a turbulent channel flow and found strong difference in both their orientation and rotation rates compared with straight fibres. We note that, in all previous studies focused on non-spherical particles in turbulent shear flows, gravity effects were deemed negligible, due to the small particle size, the small density ratio or both.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of inertial fibres and disks in a turbulent boundary layer

Baker

Coletti²

2022

J. Fluid Mech.

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We study experimentally the behaviour of negatively buoyant disks and fibres in a turbulent boundary layer. The regime is relevant to the transport of natural sediment or plastic particles in water, with density ratio $\rho _p/\rho _f \sim O(1)$ , major axis lengths $D_p^+ \sim 50$ , friction Stokes numbers $\mbox { {St}}^+ \sim O(10)$ and friction Reynolds number $\mbox { {Re}}_\tau = 620$ . The translational and rotational motion, as well as concentration and dispersion, are compared with those of spheres of similar inertia. Disks and fibres both oversample high-speed fluid near the wall, in agreement with particle-resolved numerical simulations. Fibres tend to orient mostly in the streamwise direction while disks maintain their symmetry axis quasi-normal to the wall. This alignment is more stable for disks than for fibres: the latter undergo strong tumbling near the wall in response to the mean shear and turbulent fluid velocity fluctuations, whereas the former wobble about their preferential wall-normal orientation. The translational and rotational accelerations indicate that, despite the nominal relaxation times being similar, the disks are slower than the fibres in responding to wall turbulence. For both, wall contact causes strong and intermittent tumbling. The concentration profiles follow Rouse–Prandtl theory over a limited portion of the boundary layer, deviating near the wall and in the outer region. This is largely due to the non-uniform settling velocity, which decreases steeply approaching the wall for all particle types. This is, in turn, a consequence of the reduced particle diffusivity, which closely matches the profile of the eddy viscosity.

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