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Fluid Dynamics Seminar

Monday, April 10th, 2006, 11:30 AM
Cullimore Lecture Hall, Room 611
New Jersey Institute of Technology

Periodic motion of body in high and low Reynolds numbers flow

Sunny Jung

Applied Math Laboratory, Courant Institute New York University

Abstract

In Part I, we study the behavior of an elastic loop in high Reynolds number flow. The deformable loop is wetted into the soap film and is held fixed at a single point against an oncoming flow. We interpret this system as a two-dimensional flexible body moving in a two-dimensional flow. The loop is deformed by the flow, and this coupled fluid-structure system shows bistability, with both stationary and oscillatory states. In its stationary state, the loop remains essentially motionless and its fluid wake is a von Karman vortex street. In its oscillatory state, the loop sheds two vortex dipoles within each oscillation period, and the oscillation frequency of the loop is linearly proportional to the flow velocity. Yet more complicated vortical wake patterns are observed at higher flow velocities. In Part II, we consider the flow-body interaction problem of periodic sedimentation in low Reynolds number regime. We have conducted experiments of the interactions of two identical disks falling through a Stokesian (very viscous) fluid. Their interaction can produce a surprising periodic motion of bodies. As they fall, they rotate in synchrony with their mutually induced motion. This dynamics is reproduced by a range of body types, including hemi-spheres, rods, and cubes. Currently, we are studying perturbations of this basic system that are relevant to locomotion of micro-organisms (such as bacteria) by their helical flagella.