Journal
JOURNAL OF FLUID MECHANICS
Volume 901, Issue -, Pages -Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/jfm.2020.547
Keywords
particle/fluid flow; turbulence simulation
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Funding
- Vetenskapsradet [2017-03865]
- grant 'Bottlenecks for particle growth in turbulent aerosols' from the Knut and Alice Wallenberg Foundation [KAW 2014.0048]
- joint China-Sweden mobility programme (NSFC-STINT) [11911530141, CH2018-7737]
- Natural Science Foundation of China [11702158, 91752205]
- Institute for Guo Qiang of Tsinghua University [2019GQG1012]
- Swedish Research Council [2017-03865] Funding Source: Swedish Research Council
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In homogeneous isotropic turbulence, slender rods are known to align with the Lagrangian stretching direction. However, how the degree of alignment depends on the aspect ratio of the rod is not understood. Moreover, particle-laden flows are often anisotropic and inhomogeneous. Therefore we study the alignment of rods with the Lagrangian stretching direction in a channel flow, which is approximately homogeneous and isotropic near the centre but inhomogeneous and anisotropic near the walls. Our main question is how the distribution of relative angles between a rod and the Lagrangian stretching direction depends on the aspect ratio of the rod and upon the distance of the rod from the channel wall. We find that this distribution exhibits two regimes: a plateau at small angles corresponding to random uncorrelated motion, and power-law tails due to large excursions. We find that slender rods near the channel centre align better with the Lagrangian stretching direction compared with those near the channel wall. These observations are explained in terms of simple statistical models based on Jeffery's equation, qualitatively near the channel centre and quantitatively near the channel wall. Lastly we discuss the consequences of our results for the distribution of relative angles between the orientations of nearby rods (Zhao et al., Phys. Rev. Fluids, vol. 4, 2019, 054602).
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