Accelerating fishes increase propulsive efficiency by modulating vortex ring geometry

Area of Science:

• Biomechanics and Fluid Dynamics of Aquatic Locomotion
• Comparative Animal Physiology
• Robotics and Bio-inspired Engineering

Background:

• Steady swimming strategies in aquatic animals are well-understood.
• Mechanisms of forward acceleration in swimming animals remain largely unknown.
• Significant diversity exists in steady swimming behaviors across species.

Purpose of the Study:

• To investigate the fundamental differences between steady swimming and forward acceleration.
• To identify a conserved hydrodynamic principle governing aquatic acceleration.
• To explore how propulsive efficiency is achieved during acceleration.

Main Methods:

• Integration of biomechanics, fluid dynamics, and robotics principles.
• Empirical analysis of fish swimming patterns during acceleration.
• Examination of vortex ring geometry and its relation to thrust generation.

Main Results:

• Behavioral diversity in steady swimming collapses into a single pattern during acceleration.
• Tail kinematics during acceleration enhance propulsive efficiency by altering vortex ring geometry.
• Propulsion can be increased without a corresponding increase in vortex ring size.

Conclusions:

• A fundamental hydrodynamic principle underlies aquatic forward acceleration.
• This principle appears conserved across aquatic, undulatory vertebrates.
• Findings challenge current understanding of acceleration hydrodynamics.