On the thrust generation and wake structures of two travelling-wavy foils

This paper presents a systematic work focused on the thrust generation and wake structures of two travelling-wavy foils with tandem, parallel and staggered arrangements, therein presenting essential information about actual schooling fish. The fluid dynamics around two identical foils arranged with a dimensionless horizontal gap, G_x, and vertical gap, G_y, are investigated at Reynolds number Re=2×10⁵. The wake structures are classified into proximity interference, wake interference, proximity and wake interference, and no interference associated with thrust generation. Based on numerical computations, we find that G_x significantly affects the re-organisation of the vortex shedding from the leading and following foils, resulting in various propulsive forces acting on the foils. Moreover, G_y causes a result whereby the vortex shedding from the leading foil deflects towards the flow behind the following foil, leading to a slight change in the thrust generation for both travelling-wavy foils. This work is helpful for guiding the queue control of multiple bio-inspired underwater robots.