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Open AccessArticle

Thrust and Hydrodynamic Efficiency of the Bundled Flagella

1
Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
2
Department of Mechanical Engineering, Koc University, Istanbul 34450, Turkey
3
Department of Mechanical Engineering, National Cheng Kung University, Tainan 701, Taiwan
4
Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
5
Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Stuttgart 70569, Germany
*
Author to whom correspondence should be addressed.
Micromachines 2019, 10(7), 449; https://doi.org/10.3390/mi10070449
Received: 29 April 2019 / Revised: 23 May 2019 / Accepted: 26 May 2019 / Published: 4 July 2019
(This article belongs to the Section B:Biology and Biomedicine)
The motility mechanism of prokaryotic organisms has inspired many untethered microswimmers that could potentially perform minimally invasive medical procedures in stagnant fluid regions inside the human body. Some of these microswimmers are inspired by bacteria with single or multiple helical flagella to propel efficiently and fast. For multiple flagella configurations, the direct measurement of thrust and hydrodynamic propulsion efficiency has been challenging due to the ambiguous mechanical coupling between the flow field and mechanical power input. To address this challenge and to compare alternative micropropulsion designs, a methodology based on volumetric velocity field acquisition is developed to acquire the key propulsive performance parameters from scaled-up swimmer prototypes. A digital particle image velocimetry (PIV) analysis protocol was implemented and experiments were conducted with the aid of computational fluid dynamics (CFD). First, this methodology was validated using a rotating single-flagellum similitude model. In addition to the standard PIV error assessment, validation studies included 2D vs. 3D PIV, axial vs. lateral PIV and simultaneously acquired direct thrust force measurement comparisons. Compatible with typical micropropulsion flow regimes, experiments were conducted both for very low and higher Reynolds (Re) number regimes (up to a Re number = 0.01) than that are reported in the literature. Finally, multiple flagella bundling configurations at 0°, 90° and 180° helical phase-shift angles were studied using scaled-up multiple concentric flagella thrust elements. Thrust generation was found to be maximal for the in-phase (0°) bundling configuration but with ~50% lower hydrodynamic efficiency than the single flagellum. The proposed measurement protocol and static thrust test-bench can be used for bio-inspired microscale propulsion methods, where direct thrust and efficiency measurement are required. View Full-Text
Keywords: flagellar propulsion; bacteria locomotion; microswimmer; particle image velocimetry; computational fluid dynamics flagellar propulsion; bacteria locomotion; microswimmer; particle image velocimetry; computational fluid dynamics
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Danis, U.; Rasooli, R.; Chen, C.-Y.; Dur, O.; Sitti, M.; Pekkan, K. Thrust and Hydrodynamic Efficiency of the Bundled Flagella. Micromachines 2019, 10, 449.

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