Numerical study to evaluate the important parameters affecting the hydrodynamic performance of manta ray's in flapping motion

Abstract

Manta ray swimming or bio-inspiration propulsion system, as a special type of marine propulsion system, is used for submersible vehicles that require high-speed maneuverability and stability, such as glider and AUV. In a manta ray swimming, the thrust force is generated by a couple of undulation and oscillation of wing, so that the direction of undulation wave and oscillation is upright and perpendicular to the direction of thrust force, respectively. It is possible to combine these two movement modes (flapping motion) on the three-dimensional model without considering the effects of wing twisting and flexibility to simplify and better understand the physical behaviors or special study of this movement on the manta rays as a marine glider. This study uses the computational fluid dynamics (CFD) tool to numerically simulate the complex unsteady vortical structure of flow due to the manta ray's flapping motion. The incompressible Navier-Stokes equations are solved using a pressure-based finite-volume method. In this research, the effect of kinematic parameters such as Strouhal number, non-dimensional heaving amplitude (h*), the maximum angle of attack (α0), the oscillation velocity on hydrodynamic performance during flapping motion is studied by applying a couple of heaving and pitching movement on manta ray mid-section (2D) and manta ray model (3D). The results show that although both thrust production and power consumption values are low in the 3D model, they attain higher efficiency than the 2D model.