Rotational propulsion enabled by inertia

• Published in: The European physical journal. E, Soft matter and biological physics Vol. 37; no. 7; p. 16
• Main Authors: Nadal, François, Pak, On Shun, Zhu, LaiLai, Brandt, Luca, Lauga, Eric
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-07-2014; EDP Sciences
• Subjects: 2 spheres; arbitrary shape; Bacteriology; Biological and Medical Physics; Biological and medical sciences; Biophysical Phenomena; Biophysics; Cell Movement; Cell physiology; ciliary; Complex Fluids and Microfluidics; Complex Systems; flapping flight; Fundamental and applied biological sciences. Psychology; Hydrodynamics; Microbiology; microfluidics; migration; Models, Biological; Models, Theoretical; Molecular and cellular biology; Motility and taxis; Motility, taxis; Motion; Nanotechnology; particle; Physics; Physics and Astronomy; Polymer Sciences; Regular Article; Rotation; small reynolds numbers; Soft and Granular Matter; Surfaces and Interfaces; Thin Films; Viscosity; viscous-fluid; Soft Matter: Colloids and Nanoparticles; Viscoelastic fluid; Low Reynolds number; Motility; Bacteria; Numerical simulation; Inertia; Microorganism; Cell; Modeling
• ISSN: 1292-8941; 1292-895X; 1292-895X
• DOI: 10.1140/epje/i2014-14060-y

The fluid mechanics of small-scale locomotion has recently attracted considerable attention, due to its importance in cell motility and the design of artificial micro-swimmers for biomedical applications. Most studies on the topic consider the ideal limit of zero Reynolds number. In this paper, we investigate a simple propulsion mechanism --an up-down asymmetric dumbbell rotating about its axis of symmetry-- unable to propel in the absence of inertia in a Newtonian fluid. Inertial forces lead to continuous propulsion for all finite values of the Reynolds number. We study computationally its propulsive characteristics as well as analytically in the small-Reynolds-number limit. We also derive the optimal dumbbell geometry. The direction of propulsion enabled by inertia is opposite to that induced by viscoelasticity.
Graphical abstract