With the advancement of underwater vehicles, evolving mission requirements, and payload space demands, extra-large unmanned underwater vehicles (XLUUV) have emerged as a new research focus. Distinct from traditional underwater vehicles like submarines, the most noticeable change in XLUUV is the transition from a rotating hull to a square-like hull, and the sail exhibits a flattening trend, yet research on this topic remains scarce. This work investigates the influence and characteristics of the XLUUV appendages on hydrodynamics and flow noise. The flow is captured using the improved delayed detached eddy simulation, and flow noise is obtained using the Ffowcs Williams–Hawkings equation. The study indicates that the sail primarily influences the performance of the hull and the propulsion, while the fin has a relatively minor effect. The sail alters the originally symmetrical wake field configuration, with the flattened sail generating horseshoe vortices distinct from traditional topologies. Compared to the sail located at the bow or parallel section, the sail positioned at the stern of the hull alters the originally symmetrical wake field configuration. The resulting flow disturbances bypass the dissipation and attenuation effects provided by traditional protruding structures, being rapidly drawn into the propulsion system. This intensifies the pulsating forces between the rotor and stator, generating stronger fluid noise. Second, the X-type fin resides within the low-velocity wake generated by the four edges of the square hull, thereby weakening the fin's disturbance to the overall flow field.
He et al. (2026) studied this question.