Research on localization of noise sources in boundary layer transition at the bow of underwater vehicle

The boundary layer transition at the bow of an underwater vehicle (UV) is one of the major sources of the fairing self-noise. To study the noise characteristics of the boundary layer transition at the bow of UV and the sound source locations, a scaled SUBOFF model was adopted for the experimental study in a high-speed water tunnel. The inflow velocity of the water tunnel test section was 3 – 7 m/s, and the Reynolds number based on the model length was about 10⁷. In addition, fourteen dynamic pressure sensors were arranged on the bow surface to measure the fluctuating pressure field within the region of laminar, transition and turbulent boundary layers. A phased microphone array was employed to locate the three-dimensional sound source at the bow of SUBOFF. The localization method adopts a functional beamforming method based on time-frequency transformation. The experimental results demonstrate that the transition position of the bow boundary layer moves forward synchronously with the increase of the incoming flow speed. Meanwhile, the amplitude of the mid-frequency component of the fluctuating pressure spectrum significantly rise. Furthermore, the results of sound source location show that the three-dimensional sound source presents a ring shape, and the streamwise position of the sound source almost coincides with the transition position of the boundary layer. This indicates that the transition region of the boundary layer is the main noise source in the bow region of the underwater vehicle.