Group hydrodynamic analysis of two manta rays under spacing and phase-difference coupling

Highly biosimilar manta ray morphological and kinematic models are first established, followed by a numerical study of the hydrodynamic characteristics of two manta rays swimming in tandem under the same/reverse phase-difference conditions based on the immersed boundary method. The results show that, compared to single swimming, under the same/reverse phase-difference conditions, the propulsive performance of leader manta rays are all significantly improved only when the tandem spacing is small (thrust increase up to 4.27%, efficiency increase up to 4.76%), while the propulsive performance curves of follower show fluctuating variation with the change of the spacing. It is especially worth noting that when the tandem spacing is not conducive to improving the propulsive performance, it can be improved by adjusting the motion phase difference, to realize that the wake between the individuals can be converted from collision interference to absorption and fusion, and to realize that the propulsive performance can be changed from inferior to superior. The findings of this paper provide a new idea for improving the underwater vehicle group propulsion performance based on coupled regulation of formation and motion parameters.