Statistics of rigid fibers in strongly sheared turbulence

Abstract

Practically all flows are turbulent in nature and contain some kind of irregularly-shaped particles, e.g. dirt, pollen, or life forms such as bacteria or insects. The effect of the particles on such flows and vice-versa are highly non-trivial and are not completely understood, particularly when the particles are finite-sized. Here we report an experimental study of millimetric fibers in a strongly sheared turbulent flow. We find that the fibers show a preferred orientation of −0.38π ± 0.05π (−68 ± 9 • ) with respect to the mean flow direction in high-Reynolds number Taylor-Couette turbulence, for all studied Reynolds numbers, fiber concentrations, and locations. Despite the finite-size of the anisotropic particles, we can explain the preferential alignment by using Jefferey's equation, which provides evidence of the benefit of a simplified point-particle approach. Furthermore, the fiber angular velocity is strongly intermittent, again indicative of point-particle-like behavior in turbulence. Thus large anisotropic particles still can retain signatures of the local flow despite classical spatial and temporal filtering effects.

Rotation of anisotropic particles in Rayleigh–Bénard turbulence

“…The advancement of knowledge has followed two main paths: (i) refinements in the particle description including hydrodynamic forces due to inertia, finite-size and shape (Chevillard & Meneveau 2013; Parsa & Voth 2014; Kramel et al 2016; Pujara & Variano 2017; Bounoua, Bouchet & Verhille 2018), or external forces such as gravity (Marchioli, Fantoni & Soldati 2010; Gustavsson et al 2017); (ii) exploration of different fluid flows, from laboratory-scale turbulence to geophysical settings. The second aspect is still largely uncharted, while many studies are available for the above-mentioned HIT condition, only a handful of works cover the topics of bounded turbulence (Mortensen et al 2008; Marchioli & Soldati 2013; Challabotla, Zhao & Andersson 2015; Zhao et al 2015; Bakhuis et al 2019), or surface flows (DiBenedetto, Ouellette & Koseff 2018). The fact that hitherto no study exists for thermally driven turbulence (so relevant for environmental and geophysical applications) provides a motivation for the present work.…”

Anisotropic particles in two-dimensional convective turbulence

“…However, while the phenomenology of orientations is now clear for homogeneous and isotropic turbulent flows (at least for particles of weak inertia), much less explored remains the case of non-homogeneous turbulent flows 1 . A recent step in this direction has been made in [14][15][16][17] where prolate particles have been numerically evolved in a turbulent channel flow and in 18 where rigid fibers have been experimentally tracked in a high-Reynolds number Taylor-Couette flow. In this study we extend the investigation of anisotropic particle dynamics to the paradigmatic case of turbulent convection in the Rayleigh-Bénard (RB) system, which displays both an a) Electronic mail: enrico.calzavarini@polytech-lille.fr inhomogeneous and anisotropic flow.…”

The assembly of freely moving rigid fibres measures the flow velocity gradient tensor

“…Focusing on the latter framework, several investigations concerned with both homogeneous isotropic turbulence (Parsa et al 2012;Ni et al 2015;Sabban, Cohen & van Hout 2017) as well as wall-bounded turbulent flows (Marchioli, Fantoni & Soldati 2010;Marchioli, Zhao & Andersson 2016) reveal useful insights on the preferential alignment experienced by fibres and the correlation statistics between their orientation and vorticity. Additionally, Gustavsson et al (2019) recently focused on the settling of small prolate particles, while the orientation of rod-like particles in Taylor-Couette turbulence was analysed by Bakhuis et al (2019).…”