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Rotations and accumulation of ellipsoidal microswimmers in isotropic turbulence

Published online by Cambridge University Press:  12 January 2018

N. Pujara Open the ORCID record for N. Pujara [Opens in a new window] ,
M. A. R. Koehl  and
E. A. Variano
N. Pujara*
Affiliation:
Department of Civil and Engineering, University of California, Berkeley, CA 94720, USA
M. A. R. Koehl
Affiliation:
Department of Integrative Biology, University of California, Berkeley, CA 94720, USA
E. A. Variano
Affiliation:
Department of Civil and Engineering, University of California, Berkeley, CA 94720, USA
*
†Email address for correspondence: pujara@berkeley.edu
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Abstract

Aquatic micro-organisms and artificial microswimmers locomoting in turbulent flow encounter velocity gradients that rotate them, thereby changing their swimming direction and possibly providing cues about the local flow environment. Using numerical simulations of ellipsoidal particles in isotropic turbulence, we investigate the effects of body shape and swimming velocity on particle motion. Four particle shapes (sphere, rod, disc and triaxial ellipsoid) are investigated at five different swimming velocities in the range $0\leqslant V_{s}\leqslant 5u_{\unicode[STIX]{x1D702}}$, where $V_{s}$ is the swimming velocity and $u_{\unicode[STIX]{x1D702}}$ is the Kolmogorov velocity scale. We find that anisotropic, swimming particles preferentially sample regions of lower fluid vorticity than passive particles do, and hence they accumulate in these regions. While this effect is monotonic with swimming velocity, the particle enstrophy (variance of particle angular velocity) varies non-monotonically with swimming velocity. In contrast to passive particles, the particle enstrophy is a function of shape for swimming particles. The particle enstrophy is largest for triaxial ellipsoids swimming at a velocity smaller than $u_{\unicode[STIX]{x1D702}}$. We also observe that the average alignment of particles with the directions of the velocity gradient tensor are altered by swimming leading to a more equal distribution of rotation about different particle axes.

JFM classification

Turbulent Flows: Isotropic turbulence Biological Fluid Dynamics: Micro-organism dynamics
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 838 , 10 March 2018 , pp. 356 - 368
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Copyright
© 2018 Cambridge University Press 

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