title: 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 nonlocal 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 is established. Comparing our results with data for flagellated bacteria suggests that this instability may be exploited in nature for physiological purposes.
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: M K
authors.initials: MK
authors.lastname: Jawed
authors.affiliation: Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: N K
authors.initials: NK
authors.lastname: Khouri
authors.affiliation: Department of Computer Science, Columbia University, New York, New York 10027, USA.
authors.forename: F
authors.initials: F
authors.lastname: Da
authors.affiliation: Department of Computer Science, Columbia University, New York, New York 10027, USA.
authors.forename: E
authors.initials: E
authors.lastname: Grinspun
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.|Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: P M
authors.initials: PM
authors.lastname: Reis
mesh_terms: D018407:Bacterial Physiological Phenomena; D008124:Locomotion; D008954:Models, Biological; D013550:Swimming; D014783:Viscosity