Fluid and Biodynamics Seminar: Bio-inspired Flexible Nozzle Design for Enhanced Underwater Propulsion

Unlike conventional rigid nozzles, biological propulsion systems in cephalopods utilize flexible nozzles that interact with jet flows. We investigated fluid-structure interaction mechanisms of flexible nozzles to enhance underwater propulsion performance. We developed experimental systems using flexible nozzles with varying stiffness and derived governing equations that re-vealed optimal wave speed of approximately 3 for maximum jet performance, achieving up to 300% improvement in jet impulse for pulsed jets. To validate practical applications, we tested a piston-actuated underwater vehicle with flexible nozzles attached at the outlet, demonstrating maximum performance at the predicted optimal wave speed. Additionally, water jet tests in air showed that flexible nozzles create 110% higher jet columns compared to rigid nozzles when operating at optimal conditions. Biological validation using California market squids confirmed passive wave propagation mechanisms even after neural severing. For design optimization, Bayesian optimization with 3D-printed nozzles yielded 7% thrust enhancement, with locally opti-mal designs converging on biological-like geometries featuring high tip curvature. This research demonstrates that flexible nozzles significantly enhance propulsion through passive fluid-structure interaction, providing a new paradigm for bio-inspired underwater vehicle design with applications in marine robotics and autonomous underwater vehicles.