Investigation on Thrust Force Conversion Method of Oscillating Caudal Fin Based on Wake Vortex Field Structure

Area of Science:

• Fluid Dynamics
• Bio-inspired Propulsion
• Robotics

Background:

• Understanding the hydrodynamics of oscillating fins is crucial for developing efficient bio-inspired propulsion systems.
• Previous studies have focused on rigid fins, but the complex wake dynamics of flexible fins remain less understood.

Purpose of the Study:

• To investigate the wake field generated by a flexible oscillating caudal fin.
• To develop and validate a quantitative model for converting wake field characteristics into thrust force.
• To assess the accuracy of the proposed model by comparing its predictions with experimental measurements.

Main Methods:

• Employed the Digital Particle Image Velocimetry (DPIV) system to capture wake field data.
• Utilized a self-developed program to calculate velocity circulation, vortex radius, and vortex pair spacing.
• Introduced a three-dimensional vortex ring chain model and a conversion model based on vortex dynamics theory.

Main Results:

• Presented detailed vorticity distributions across various Strouhal numbers.
• Quantified key wake parameters including velocity circulation and vortex ring radius.
• Demonstrated low relative errors (5.86% and 3.44%) when comparing model-derived thrust force with experimental data from a tricomponent balance system.

Conclusions:

• The developed thrust force conversion model for flexible oscillating caudal fins is accurate and reliable.
• The study provides an effective method for quantitative conversion between caudal fin flow fields and thrust force.
• Findings contribute to the design and optimization of underwater vehicles utilizing oscillating fin propulsion.