Propulsion of a combined heaving and trailing-edge morphing foil for bio-inspired applications

Abstract

Locomotion of aquatic animals involves flapping of their body to generate lift and thrust. Through evolution, they have mastered their ability to move through complex environments in an energy-efficient manner. A crucial component of this movement is the ability to actively bend their bodies to generate maximum thrust. This motion is widely termed as morphing. A simplification of this motion is implemented for a foil in this study to realize a thrust-generating bio-inspired device. The propulsive performance of the heaving foil undergoing a prescribed trailing-edge morphing is numerically studied by a stabilized finite element moving mesh formulation. The effects of the morph position and amplitude on the flow dynamics and propulsion of the foil are investigated in the present work. The position of trailing-edge morphing varies from the leading edge to half of the foil's chord, whereas the morph amplitude varies from 10 ° to 60 ° at the trailing edge. The instantaneous thrust is analyzed with vorticity plots and surface pressure diagrams. Within the parametric space, it is found that the foil is highly efficient in generating propulsive forces at high morph amplitudes and low morph positions. The interplay between the thrust-generating leading-edge vortex (LEV) and the drag-inducing trailing-edge vortex (TEV), which governs the thrust cycle of a morphing–heaving foil, is elucidated. It is observed that the LEV-induced thrust is higher at low morph positions, while the TEV-induced drag is dominant at high morph amplitudes. An ideal balance of these opposing effects of LEV and TEV occurs at the lowest morph position and intermediate morph amplitudes, emphasizing the optimal flexibility for the maximum propulsive performance of the foil.