The most efficient metazoan swimmer creates a 'virtual wall' to enhance performance
Document Type
Article
Publication Title
Proceedings of the Royal Society B: Biological Sciences
Publication Date
1-13-2021
Abstract
It has been well documented that animals (and machines) swimming or flying near a solid boundary get a boost in performance. This ground effect is often modelled as an interaction between a mirrored pair of vortices represented by a true vortex and an opposite sign 'virtual vortex' on the other side of the wall. However, most animals do not swim near solid surfaces and thus near body vortex-vortex interactions in open-water swimmers have been poorly investigated. In this study, we examine the most energetically efficient metazoan swimmer known to date, the jellyfish Aurelia aurita, to elucidate the role that vortex interactions can play in animals that swim away from solid boundaries. We used high-speed video tracking, laser-based digital particle image velocimetry (dPIV) and an algorithm for extracting pressure fields from flow velocity vectors to quantify swimming performance and the effect of near body vortex-vortex interactions. Here, we show that a vortex ring (stopping vortex), created underneath the animal during the previous swim cycle, is critical for increasing propulsive performance. This well-positioned stopping vortex acts in the same way as a virtual vortex during wall-effect performance enhancement, by helping converge fluid at the underside of the propulsive surface and generating significantly higher pressures which result in greater thrust. These findings advocate that jellyfish can generate a wall-effect boost in open water by creating what amounts to a 'virtual wall' between two real, opposite sign vortex rings. This explains the significant propulsive advantage jellyfish possess over other metazoans and represents important implications for bio-engineered propulsion systems.
Volume
288
Issue
1942
DOI
10.1098/rspb.2020.2494
Recommended Citation
Gemmell, B., Du Clos, K., Colin, S., Sutherland, K., & Costello, J. (2021). The most efficient metazoan swimmer creates a 'virtual wall' to enhance performance. Proceedings of the Royal Society B: Biological Sciences, 288 (1942) https://doi.org/10.1098/rspb.2020.2494
ISSN
09628452
E-ISSN
14712954