Researchers from the Department of Mechanical Engineering at the University of British Columbia have unveiled groundbreaking insights into the hydrodynamic secrets of fish swimming, with significant implications for the design of bio-inspired underwater robots. The team, led by Dr. Zahra Maleksabet and including Maham Kamran, Ali Tarokh, and Muhammad Saif Ullah Khalid, has conducted a detailed study on how different swimming maneuvers influence the vortex dynamics and hydrodynamic forces experienced by fish.
The study focuses on two distinct swimming styles: anguilliform and carangiform. Anguilliform swimmers, like eels, generate traveling waves along their entire bodies, while carangiform swimmers, such as jack fish, concentrate their motion near their tails. The researchers specifically examined the burst-and-coast maneuver, an intermittent swimming style where fish alternate between bursts of undulatory motion and periods of gliding. This maneuver is known for its energy efficiency but also significantly alters the wake structure and hydrodynamic forces.
Using three-dimensional simulations at a Reynolds number of 3000, the team analyzed the swimming patterns of an eel and a jack fish. They varied the duty cycle (DC), which represents the proportion of time spent in active swimming versus gliding, and the Strouhal number (St), a dimensionless number describing the oscillating motion of the tail. The simulations revealed that the burst-and-coast motion in both swimmers produces bow-shaped wakes. As the duty cycle increases to 1.0, the two rows of vortices on either side of the wake become more coherent, resembling the wake of continuously undulating swimmers.
Interestingly, the study found that intermittent motion at a higher Strouhal number generates more drag compared to continuous undulatory kinematics. To further investigate this behavior, the researchers quantified the strengths of the vortices produced around the two swimmers and analyzed their instantaneous kinematic metrics. They also conducted a detailed analysis of the role of different body sections in the production of unsteady streamwise forces.
The insights gained from this study provide crucial connections between the swimmers’ physiologies, their kinematics, and the governing vortex dynamics. These findings are poised to significantly impact the design of next-generation autonomous bio-inspired underwater robots. By understanding how different swimming maneuvers influence hydrodynamic efficiency, engineers can develop more effective and energy-efficient robotic systems that mimic the natural swimming styles of fish. This research not only advances our scientific understanding of fish locomotion but also paves the way for innovative advancements in marine robotics. Read the original research paper here.