Improvement of Propulsive Efficiency of a Tandem Aerofoil Following Fishtailed Motion

To enhance performance in both aerial and aquatic locomotion, many bird flocks and fish schools adopt a tandem arrangement of wings or fins. Recent studies in this field, particularly those involving fluttering foils, remain challenging due to their complex flow dynamics. In this work, the focus shifts from the conventional flapping pattern characterized by vertical heave and pitch motions to a novel fishtail flapping trajectory for tandem hydrofoils. The foil motion is simulated using an ALE framework in conjunction with a dynamic mesh, allowing the incompressible Navier–Stokes equations to be solved for the surrounding flow field. Alongside trajectory analysis, the effects of Strouhal number (St) and foil phase angle (φ) on thrust generation are examined. Findings indicate that employing a tandem flapping foil configuration with elliptical or fishtail motion can substantially improve both thrust output and propulsive efficiency.