Numerical studies are presented on the propulsive performance and vortex dynamics
of multiple hydrofoils pitching in an in-line configuration. The study is motivated by
the quest to understand the hydrodynamics of multiple fin–fin interactions in fish
swimming. Using the flow conditions (Strouhal and Reynolds numbers) obtained from
a solitary pitching foil of zero net thrust, the effect of phase differences between
neighboring foils on the hydrodynamic performance is examined both in position-fixed
two- and three-foil systems at Reynolds number Re = 500. It is found that the threefoil
system achieves a thrust enhancement up to 118% and an efficiency enhancement
up to 115% compared to the two-foil system. Correspondingly, the leading-edge vortex
(LEV) and the trailing-edge vortex (TEV) of the hindmost foil combine to form a ‘2P’
wake structure behind the three-foil system with the optimal phase differences instead
of a ‘2S’ wake, a coherent wake pattern observed behind the optimal two-foil system.
The finding suggests that a position-fixed three-foil system can generate a ‘2P’ wake
to achieve the maximum thrust production and propulsive efficiency simultaneously
by deliberately choosing the undulatory phase for each foil. When increasing Reynolds
number to 1000, though the maximum thrust and propulsive efficiency are not achieved
simultaneously, the most efficient case still produces more thrust than most of the other
cases. Besides, the study on the effects of three-dimensionality shows that when the foils
have a larger aspect ratio, the three-foil system has a better hydrodynamic performance,
and it follows a similar trend as the two-dimensional (2D) foil system. This work aids
in the future design of high-performance underwater vehicles with multiple controlled
propulsion elements.
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Body Shape Effects on the Hydrodynamic Performance of Bio-Inspired Undulating Swimmers
In this study, numerical simulations are performed to study the effects of body shape on propulsive performance in a carangiform-like swimming motion. A focus is given to the variation in performance due to changes in the maximum thickness, maximum thickness location, leading-edge radius, and boattail angle of an undulating foil. An immersed boundary method-based incompressible flow solver is implemented to solve for the propulsive performance of two-dimensional undulating foils. The resulting flow simulations yield the thrust, drag, efficiency, and flow for each body shape. From this study, we have found that better propulsive performance comes from a thinner maximum thickness, a maximum thickness location closer to the head of the fish, a narrower boattail angle, and a larger leading-edge radius. Particular care is given to the analysis of the boattail angle, because of the surprising and significant results. In changing only the boattail angle the efficiency is shown to vary by 10.3%. Changes in the leading-edge radius varies the efficiency by 4.4%, the maximum thickness by 4.0%, and the maximum thickness location along the body by 5.0%. The large improvement observed in the thinner boattail angle cases are caused by the increased curvature around the middle of the fish body leading to a high-pressure region at the tail that improves the thrust performance. The results can be used to improve understanding of fish body shapes observed in nature as well as better informing the design of bioinspired underwater robots.
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- Award ID(s):
- 1931929
- NSF-PAR ID:
- 10473194
- Publisher / Repository:
- Fluids Engineering Division Summer Meeting
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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