title: Viscous pumping inspired by flexible propulsion.
abstract: Fluid-suspended microorganisms have evolved different swimming and feeding strategies in order to cope with an environment dominated by viscous effects. For instance, ciliated organisms rely on the collective motion of flexible appendages to move and feed. By performing a non-reciprocal motion, flexible filaments can produce a net propulsive force, or pump fluid, in the absence of inertia. Inspired by such a fundamental concept, we propose a strategy to produce macroscopic pumping and mixing in creeping flow. We measured experimentally the net motion of a Newtonian viscous fluid induced by the reciprocal motion of a flapper. When the flapper is rigid no net motion is induced. In contrast, when the flapper is made of a flexible material, a net fluid pumping is measured. We quantify the effectiveness of this pumping strategy and show that optimal pumping is achieved when the length of the flapper is on the same order as the elasto-hydrodynamic penetration length. We finally discuss the possible applications of flexible impellers in mixing operations at low Reynolds numbers.
authors.affiliation: Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apdo. Postal 70-360 México D.F. 04510, Mexico.
authors.forename: Roger M
authors.initials: RM
authors.lastname: Arco
authors.forename: J Rodrigo
authors.initials: JR
authors.lastname: Vélez-Cordero
authors.forename: Eric
authors.initials: E
authors.lastname: Lauga
authors.forename: Roberto
authors.initials: R
authors.lastname: Zenit
mesh_terms: D058500:Animal Fins / Q000502:physiology*; D000818:Animals; D032701:Biomimetics / Q000295:instrumentation* / Q000379:methods; D055119:Elastic Modulus; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D012212:Rheology / Q000295:instrumentation* / Q000379:methods; D013550:Swimming / Q000502:physiology*; D014159:Transducers; D014783:Viscosity