A Study on the Drag Reduction Characteristics of Flexible Appendage Submersible During Dives

Abstract This research introduces an approach for modifying the wake structure of submersibles during descent by integrating flexible appendages onto their surface, with the goal of achieving drag reduction. To quantify the impact of these appendages on hydrodynamic drag and wake patterns, experiments employing a six-component force sensor and high-speed particle image velocimetry (PIV) were conducted on submersible models equipped with appendages of varying lengths. The findings indicate that flexible appendages can reduce drag by up to 8.7% during vertical descent. Analysis of the time-averaged and transient flow fields at a Reynolds number of 109,582 reveals that the appendages disrupt the wake vortices under vertical diving conditions. To elucidate the underlying mechanism, the proper orthogonal decomposition (POD) technique was applied. POD results demonstrate that the flexible appendages modify the vortex structure within the wake, leading to a reduction in vortex energy and a suppression of vortex shedding phenomena.