Propulsion and instability of a flexible helical rod rotating in a viscous fluid

Abstract

We combine experiments with simulations to investigate the fluid-structure interaction of a flexible helical rod rotating in a viscous fluid, under low Reynolds number conditions. Our analysis takes into account the coupling between the geometrically nonlinear behavior of the elastic rod with a non-local hydrodynamic model for the fluid loading. We quantify the resulting propulsive force, as well as the buckling instability of the originally helical filament that occurs above a critical rotation velocity. A scaling analysis is performed to rationalize the onset of this instability. A universal phase diagram is constructed to map out the region of successful propulsion and the corresponding boundary of stability are established. Comparing our results with data for flagellated bacteria suggests that this instability may be exploited in nature for physiological purposes.

5 pages, 5 figures, in press at Physical Review Letters

References in corpus (4)

• Propulsion with a Rotating Elastic Nanorod
• Shape transition and propulsive force of an elastic rod rotating in a viscous fluid
• Rotational dynamics of a soft filament: wrapping transition and propulsive forces
• Rotational dynamics of a superhelix towed in a Stokes fluid

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