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Falling styles of disks
Published online by Cambridge University Press: 19 February 2013
Abstract
We numerically investigate the dynamics of thin disks falling under gravity in a viscous fluid medium at rest at infinity. Varying independently the density and thickness of the disk reveals the influence of the disk aspect ratio which, contrary to previous belief, is found to be highly significant as it may completely change the route to non-vertical paths as well as the boundaries between the various path regimes. The transition from the straight vertical path to the planar fluttering regime is found to exhibit complex dynamics: a bistable behaviour of the system is detected within some parameter range and several intermediate regimes are observed in which, although the wake is unstable, the path barely deviates from vertical. By varying independently the body-to-fluid inertia ratio and the relative magnitude of inertial and viscous effects over a significant range, we set up a comprehensive map of the corresponding styles of path followed by an infinitely thin disk. We observe the four types of planar regimes already reported in experiments but also identify two additional fully three-dimensional regimes in which the body experiences a slow horizontal precession superimposed onto zigzagging or tumbling motions.
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- ©2013 Cambridge University Press
References
Auguste et al. supplementary movie
Falling styles of discs I*=0.16; Ar=27.8 “Autorotation(=tumbling) AR regime”
Auguste et al. supplementary movie
Falling styles of discs I*=0.48;Ar=47.9 “Helical tumbling HA regime”
Auguste et al. supplementary movie
Falling styles of discs I*=0.012; Ar=47.1 “Helcial fluttering HH regime”
Auguste et al. supplementary movie
Falling styles of discs I*0.048; Ar=25.5 “Zigzagging (=fluttering)ZZ regime”
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