Research on unsteady characteristics of different appendaged submarines flows based on dynamic mode decomposition

The unsteady flows around the submarines cause high-frequency fluctuating pressure and noise on the vehicle. Studying unsteady characteristics and establishing accurate prediction methods for Submarine unsteady flow is essential to understand flow separation-induced noise better. In this study, the SUBOFF model is taken as the research object for numerical analysis. In the speed range of 5.93kn-16kn, the vortex distribution characteristics are analyzed. During the stable flow phase, the frequency and amplitude of vorticity at different modes are established based on the DMD method. The primary mode information is used to reconstruct the flow field of the submarine. The results show that at 5.93kn-16kn speed, the unsteady characteristics of the bare hull model and sail appendages model are not prominent, and the stern appendages model and the fully appended model show regular vortex shedding and the frequency of little vortex shedding increases with increasing speed. The eigenfrequency modes reflect the unsteady characteristics of submarine winding. The mode analysis results of the fully appended model reflected the primary frequency vortex and frequency-doubled vortex are the main vortex forms of the whole appendages wake. The tail vortex of the sail merges with the stern wing vortex, making the flow field more stable.