Das, A and Shukla, RK and Govardhan, RN (2022) Contrasting thrust generation mechanics and energetics of flapping foil locomotory states characterized by a unified - Scaling. In: Journal of Fluid Mechanics, 930 .
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Abstract
Self-propelled flapping foils with distinct locomotion-enabling kinematic restraints exhibit a remarkably similar Strouhal number -Reynolds number dependence. This similarity has been hypothesized to pervade diverse forms of oscillatory self-propulsion and undulatory biolocomotion; however, its genesis and implications on the energetic cost of locomotion remain elusive. Here, using high-resolution simulations of translationally free and restrained foils that self-propel as they are pitched, we demonstrate that a generality in the - relationship can emerge despite significant disparities in thrust generation mechanics and locomotory performance. Specifically, owing to a recoil reaction induced passive heave, the fluid's inertial response to the prescribed rotational pitch, the principal source of thrust in unidirectionally free and towed configurations, ceases to produce thrust in a bidirectionally free configuration. Rather, the thrust generated from the leading edge suction mechanics self-propels a bidirectionally free pitching foil. Owing to the foregoing distinction in the thrust generation mechanics, the - relationships for the bidirectionally and unidirectionally free/towed foils are dissimilar and pitching amplitude dependent, but specifically for large reduced frequencies, converge to a previously reported unified power law. Importantly, to propel at a given mean forward speed, the bidirectionally free foil must counteract the out-of-phase passive heave through a more intense rotational pitch, resulting in an appreciably higher power consumption over the range. We highlight the critical role of thrust in introducing an offset in the - relation, and through its amplification, being ultimately responsible for the considerable disparity in the locomotory performance of differentially constrained foils. © 2022 Cambridge University Press. All rights reserved.
| Item Type: | Journal Article |
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| Publication: | Journal of Fluid Mechanics |
| Publisher: | Cambridge University Press |
| Additional Information: | The copyright for this article belongs to Aurhors |
| Keywords: | Reynolds number, Biolocomotion; Energetic costs; Flapping foil; Performance; Reynold number; Scalings; Self-propulsion; Swimming/flying; Thrust generation; Vortex-shedding, Propulsion, energetics; Reynolds number; swimming; vortex shedding |
| Department/Centre: | Division of Mechanical Sciences > Mechanical Engineering |
| Date Deposited: | 21 Dec 2021 05:47 |
| Last Modified: | 21 Dec 2021 05:47 |
| URI: | http://eprints.iisc.ac.in/id/eprint/70666 |
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