Undulating fins produce off-axis thrust and flow structures

Izaak D. Neveln, Rahul Bale, Amneet Pal Singh Bhalla, Oscar M. Curet, Neelesh A. Patankar, Malcolm A. MacIver*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

48 Scopus citations


While wake structures of many forms of swimming and flying are well characterized, the wake generated by a freely swimming undulating fin has not yet been analyzed. These elongated fins allow fish to achieve enhanced agility exemplified by the forward, backward and vertical swimming capabilities of knifefish, and also have potential applications in the design of more maneuverable underwater vehicles. We present the flow structure of an undulating robotic fin model using particle image velocimetry to measure fluid velocity fields in the wake. We supplement the experimental robotic work with highfidelity computational fluid dynamics, simulating the hydrodynamics of both a virtual fish, whose fin kinematics and fin plus body morphology are measured from a freely swimming knifefish, and a virtual rendering of our robot. Our results indicate that a series of linked vortex tubes is shed off the long edge of the fin as the undulatory wave travels lengthwise along the fin. A jet at an oblique angle to the fin is associated with the successive vortex tubes, propelling the fish forward. The vortex structure bears similarity to the linked vortex ring structure trailing the oscillating caudal fin of a carangiform swimmer, though the vortex rings are distorted because of the undulatory kinematics of the elongated fin.

Original languageEnglish (US)
Pages (from-to)201-213
Number of pages13
JournalJournal of Experimental Biology
Issue number2
StatePublished - Jan 2014


  • Bio-mimetic
  • Bio-robotics
  • Digital particle image velocimetry (DPIV)
  • Fish locomotion
  • Knifefish
  • Undulating fin propulsion

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Physiology
  • Aquatic Science
  • Animal Science and Zoology
  • Molecular Biology
  • Insect Science


Dive into the research topics of 'Undulating fins produce off-axis thrust and flow structures'. Together they form a unique fingerprint.

Cite this