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In this study, we numerically investigate the effects of the tail-beat phase differences between the trailing fish and its neighboring fish on the hydrodynamic performance and wake dynamics in a two-dimensional high-density school. Foils undulating with a wavy-like motion are employed to mimic swimming fish. The phase difference varies from 0° to 360°. A sharp-interface immersed boundary method is used to simulate flows over the fish-like bodies and provide quantitative analysis of the hydrodynamic performance and wakes of the school. It is found that the highest net thrust and swimming efficiency can be reached at the same time in the fish school with a phase difference of 180°. In particular, when the phase difference is 90°, the trailing fish achieves the highest efficiency, 58% enhancement compared with a single fish, while it has the highest thrust production, increased by 108% over a single fish, at a phase difference of 0°. The performance and flow visualization results suggest that the phase of the trailing fish in the dense school can be controlled to improve thrust and propulsive efficiency, and these improvements occur through the hydrodynamic interactions with the vortices shed by the neighboring fish and the channel formed by the side fish. In addition, the investigation of the phase difference effects on the wake dynamics of schools performed in this work represents the first study in which the wake patterns for systems consisting of multiple undulating bodies are categorized. In particular, a reversed Bénard–von Kármán vortex wake is generated by the trailing fish in the school with a phase difference of 90°, while a Bénard–von Kármán vortex wake is produced when the phase difference is 0°. Results have revealed that the wake patterns are critical to predicting the hydrodynamic performance of a fish school and are highly dependent on the phase difference.
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Wake Interactions Between Groups of Undulating Foils
The canonical motion of foils has been studied extensively in many applications, including energy harvesting. The advantage of undulating foils is often realized in their ability to positively interfere with neighboring foils. However, more research is needed in understanding different arrangements of undulating foils, along with the fluid dynamics interactions involved in enhancing the performance of the foils for this advantage to properly scale to a large number of foils. This work utilizes the concept of subgroups within a school, borrowed from biological studies of fish schools, along with an immersed boundary methodbased computational fluids solver to investigate how these larger groups of undulating foils interact. A parametric study is completed around the spacing of the back subgroup, and the vortex formation and wake structures are analyzed, revealing that the back subgroup gains efficiency via interactions with the wake of the front subgroup. The present study gives insight into how groups of undulating foils interact and uncovers mechanisms that enhance performance through their interaction.
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- Award ID(s):
- 1931929
- PAR ID:
- 10473220
- Publisher / Repository:
- American Institute of Aeronautics and Astronautics
- Date Published:
- ISBN:
- 978-1-62410-699-6
- Format(s):
- Medium: X
- Location:
- National Harbor, MD & Online
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.2514/6.2023-2292
