Sound generated by flow over two traveling wavy foils in a side-by-side arrangement

Abstract

Numerical simulations are employed to investigate the sound generated by flow over two traveling wavy foils in a side-by-side arrangement by an immersed-boundary-method-based hybrid approach. The effects of Strouhal number ( St), phase difference, and lateral spacing ( S) between the foils on the flow performance and the sound pressure field are examined. The results imply that the sound produced by a single foil is dominated by the lift dipole, and that the low-amplitude–high-frequency foil can achieve higher thrust and higher sound pressure compared to the high-amplitude–low-frequency foil. For the two side-by-side foils (i.e., an in-phase and anti-phase foil system), the sound pressure fields exhibit distinct features. Specifically, a dipole-like pattern appears during in-phase motion, whereas a monopole-like pattern exists during anti-phase motion. Moreover, the magnitude of the sound pressure increases slightly with increasing S in the in-phase case. However, the sound pressure decreases rapidly when S < 0.7 L (foil length) and then remains nearly unchanged when S > 0.7 L in the anti-phase case. Furthermore, the anti-phase foil system could improve thrust by increasing power consumption and could generate lower sound pressure compared to the in-phase one due to the distinct differences in wake patterns. The present work is expected to improve the understanding of sound-generation mechanisms of fish-like locomotion and collective motion for relevant biomimetic underwater vehicles.