Vibration and noise reduction of underwater gliders with a novel wing integrating flexible cladding and phononic crystals

As the accuracy of sensors carried by underwater gliders increases, the interference from ambient noise has drawn increasing attention. Typically, the wings of underwater gliders can produce great hydrodynamic noise when subjected to fluid loads. To reduce vibration and noise, this study designs a novel wing that combines flexible cladding and phononic crystals (PnCs). The flexible cladding allows for modulation control of the flow field surrounding the wing. The boundary velocity profile is explored to obtain the position of flow separation and the wing's resistance to the separation. The cladding characteristics are optimised to reduce the flow noise generated by the wing. The PnCs achieve vibration control of the wing with optimised lattice constant, porosity, and groove distance, reducing the flow-excited noise. In the hydrodynamic noise simulation, the novel wing reduces the noise by an average of 3.5 dB within 0–200 Hz and obtains a maximum noise reduction of 20.2 dB at 21 Hz. In addition, the noise increase of the flexible cladding wing within 111–168 Hz is greatly improved. Finally, a tank experiment was conducted using a Petrel-4000 underwater glider to confirm the accuracy of hydrodynamic noise simulation, proving the effect of the novel wing design for vibration and noise reduction.