Optimal specific wavelength for maximum thrust production in undulatory propulsion

Area of Science:

• Fluid dynamics
• Biomechanics
• Hydrodynamics

Background:

• Undulatory swimmers exhibit a wide range of body/caudal fin (BCF) propulsion methods.
• Previous research has observed but not fully explained the specific wavelength (SW) used by these swimmers.

Purpose of the Study:

• To investigate the constraint on specific wavelength (SW) in body/caudal fin (BCF) swimmers.
• To determine if an optimal specific wavelength (OSW) exists that maximizes swimming performance.
• To understand the underlying mechanisms of propulsive thrust in undulatory swimmers.

Main Methods:

• Numerical simulations of fluid-structure interaction were employed.
• Analysis of specific wavelength (SW) values across various BCF swimmers, including larval zebrafish, herring, and eels.
• Quantification of mechanisms responsible for maximum propulsive thrust.

Main Results:

• A narrow range of specific wavelength (SW) values is utilized by diverse BCF swimmers.
• An optimal specific wavelength (OSW) was identified that maximizes swimming speed and thrust.
• Observed SW values in natural swimmers closely approximate the calculated OSW.
• Mechanisms for maximum thrust align with existing hypotheses.

Conclusions:

• A universal hydrodynamic constraint related to optimal specific wavelength (OSW) governs undulatory propulsion in BCF swimmers.
• This finding provides empirical design criteria for developing efficient man-made propulsors.
• The study elucidates the evolutionary advantage of adhering to an OSW for natural swimmers.