A study on the wake structure of an ascending submersible with silk flexible appendages using continuous wavelet transform and dynamic mode decomposition

This study proposed a new method for installing silk flexible appendages on the surface of the submersible to modify the wake structure of ascending submersibles, and explored a method of drag reduction of ascending submersible. A comparative analysis of the flow structure of submersibles with varying appendage lengths was conducted to understand the disturbance characteristics of the wake flow structure of submersible, and the high-speed particle image velocimetry (PIV) measurement experiment was conducted at a Reynolds number of 6456. Analysis of the time-averaged flow field showed that the flexible appendages could disrupt the two large-scale vortices in the wake of the submersibles during the sailing process, but this ability diminished with increasing appendage length. Furthermore, continuous wavelet transform (CWT) and dynamic mode decomposition (DMD) were used to analyze the mechanism behind this phenomenon. The analysis results showed that flexible appendages based on CWT had an inhibitory effect on large-scale flow, and this effect gradually decreased with increasing appendage length. The results indicate that the flexible appendages can disrupt the wake vortex structure, reduce vortex energy, and facilitate the transition from large-scale vortex to small-scale vortex. Additionally, excessive disturbance is generated in the wake region when the flexible appendage is too long, hindering the shedding of small-scale vortices and resulting in an increase.