Abstract
A numerical investigation is conducted on the propulsive performance and acoustic characteristics of two flapping foils in tandem at Re = 200 in uniform flow using the lattice Boltzmann method combined with the immersed boundary method. The effects of phase difference and horizontal spacing on hydrodynamics and acoustics are studied. The results indicate that the propulsive performance and acoustic characteristics of the in-phase foils and anti-phase foils are completely different. As the horizontal spacing increases, the change trend of their propulsive performance is completely opposite. The propulsive performance of the in-phase foils shows a trend of first weakening and then enhancing, while the anti-phase foils show a trend of first enhancing and then weakening. For sound field, the in-phase foils exhibit a dipole-like pattern similar to that of a single foil, while it exhibits a quadrupole-like pattern for anti-phase foils. Compared to the in-phase foils and single foil, the maximum effective sound pressure value of the anti-phase foils is smaller. Meanwhile, the relationship between propulsive performance and acoustic characteristics is analyzed, and it is found that the correlation coefficients follow the same variation pattern. The presented work can offer valuable insights for designing and controlling new bio-inspired autonomous underwater vehicles aimed at suppressing flow noise.