Design, hydrodynamic analysis, and test of a manta ray-inspired soft wing for flapping wing propulsion of underwater gliders

Abstract

Mobuliform swimming of manta rays represents a unique propulsion that can potentially be applied to underwater gliders (UGs) to enhance their maneuverability while minimizing noise. Inspired by the flexible pectoral fins of manta rays, this paper proposes a novel form of integral soft wing made of silicone rubber driven by a rigid fin ray insert, instead of flexible skin supported by rigid skeleton, and designs a UG prototype with the proposed soft wings (hereinafter referred to as SWUG). The soft wings reproduce spanwise oscillation and chordwise wave in mobuliform swimming, both of which contribute to thrust generation. The fluid-structure interaction is considered to analyze how the soft wings' physical parameters affect the UGs' hydrodynamic characteristics. The optimal configurations for the airfoil, dihedral angle, and aspect ratio are determined for excellent gliding performance. Further, the kinematic-Computational Fluid Dynamics (CFD) coupling approach is applied to simulate the intricate unsteady flow field resulting from the controlled motion of the soft wings. The evolution of the flow field and the thrust generation mechanism are analyzed, and the influence of flapping kinematic parameters on thrust performance and vehicle maneuverability are determined. Finally, the prototypes of the soft wings and SWUG are constructed to measure thrust and test swimming performance. A single soft wing can generate a maximum thrust of 3.6 N, and the SWUG can reach a top speed of 0.52 m/s. Experimental results validate the simulation findings and demonstrate the effective enhancement of UGs’ maneuverability by the soft wings. This research also offers insights into motion performance improvement and bionic design for other underwater vehicles.