Numerical analysis of the effects of size ratio and relative position on two self-propelled foils in tandem arrangement

The effects of size ratio and relative position on the hydrodynamic performance of two self-propelled foils with tandem arrangement in incompressible flows were numerically investigated. Simulations were performed with the immersed boundary method (IBM), and the foils are modelled with the NACA0012 foils. Based on a systematic parameter study of the size ratio and relative position between the two foils, the swimming velocity and propulsion efficiency are discussed in detail. Vortex structures of flow field are analysed to elucidate the flow-mediated interaction. The results showed that foils do not always benefit from the hydrodynamic interaction between each other, and the size ratio has an important influence on the selection of foils' relative position to form a thrust-enhancement or energy-efficiency propulsion pattern. The smaller the size ratio, the greater the hydrodynamic benefits follower foil can obtain. As the size ratio increasing, leader foil may achieve smaller power consumption with faster forward velocity.