Effect of tail configuration on ascent stability of an underwater buoy

Aiming at the core research gap that the influence of tail configurations on the full-ascent attitude stability of deep-water-released unpowered buoys has not been revealed, the present study establishes a three-dimensional numerical model based on the Reynolds-Averaged Navier–Stokes (RANS) equations via the ANSYS Fluent platform to systematically investigate the influence of tail configuration on the buoy’s motion stability during the ascending process. Specifically, four distinct tail geometries are investigated: The Type-1 buoy (baseline design) achieves optimal motion stability but exhibits excessively high drag, substantially compromising system efficiency. The Type-2 buoy with an optimized streamlined tail reduces drag to approximately 16.93% of the Type-1 buoy value yet it exhibits significantly degraded motion stability throughout ascent and water exit, and thus may not maintain a stable attitude during the water-exit stage. Further refinements to the developed Type-3 and Type-4 buoys yield a more favorable trade-off between drag reduction and motion stability. The Type-3 buoy achieves superior motion stability, with its drag force increasing by only approximately 11.61% relative to the Type-2 buoy. The Type-4 buoy achieves the lowest overall drag; although its attitude angle fluctuation slightly exceeds that of the Type-3 buoy, it remains superior to that of the Type-2 buoy. These results indicate that streamlined tail optimization can effectively address the trade-off between hydrodynamic performance and motion stability during ascent, and provide design guidance for tail configurations of similar underwater buoys.