Streaming and mixing induced by a bundle of ciliary vibrating micro-pillars |
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Authors: | Christoph Brücker Armin Keissner |
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Institution: | (1) TU Bergakademie Freiberg, Lampadiusstrasse 4, 09599 Freiberg, Germany |
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Abstract: | Directional near-wall flow induced by the vibration of slender micro-pillars attached to a surface similar to ciliary structures
or grafted filaments is studied experimentally. The micro-pillar arrays are arranged in the form of a “V” approximating an
asymmetric fore-aft bundle shape often found in nature, too. A base-layer actuation is used to excite the micro-pillars to
oscillate in a vibratory pattern with maximum amplitude at the tips. Due to the specific shape of the bundle structure and
asymmetric boundary conditions of the oscillatory motion, the pillars perform a tilted beating motion—similar to cilia—with
a forward power stroke and a backward oriented recovery stroke or vice versa, depending on the boundary conditions of the
actuation. As a consequence of the cooperative beating motion and the fore-aft asymmetry of the shape of the bundle, a directional
streaming motion is induced by the pillars which increase with increasing streaming Reynolds number Re
S
. In addition to the net streaming effect, the flow in the space between the pillar bases exhibit a micro-scale swirling motion
around each of the structures with an efficient mixing behavior. Applied to micro-channels or wall-bounded flows, such structures
may act as locally distributed passive or active flow manipulation devices. The use of such cilia bundles in large numbers
on surfaces as passive structures for near-wall control in of boundary layer flows is feasible, too. |
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