A study on the drag reduction characteristics of flexible appendage submersibles during dives

This study presents a novel method for installing flexible appendages (hairs) on the surface of a submersible to reduce its drag as it descends from the surface to the seafloor. First, the changes in drag, Reynolds stress, turbulent kinetic energy, and time-averaged streamlines of the flow field before and after the addition of hair appendages to the submersible were analyzed using a six-component sensor and particle image velocimetry (PIV). The results indicate that, with optimal hair appendages, the drag of the submersible is reduced by 8.7% compared to a conventional submersible (0 L ), and the intensity and extent of the two large-scale eddies in the flow field decrease. Subsequently, the energy spectrum of the flow field, the dominant modes of the flow, and the energy distribution within the vortex core before and after the addition of hair appendages were analyzed using Fourier transform and proper orthogonal decomposition (POD). The results show that hair appendages of optimal length can reduce vortex frequency and energy in the flow field of a submersible. It was also found that hair appendages were able to alter the intrinsic period of the time coefficient and amplify its peak, leading to the emergence of more complex flow features.