EXPERIMENTAL INVESTIGATION INTO THE CONTROL OF FLOW-INDUCED OSCILLATIONS OF UNDERWATER APERTURE-CAVITIES

Flow-induced oscillation (FIO) of underwater aperture-cavities is one of prominent noise sources of underwater vehicles. In order to explore the effective control method and suppression characteristics of FIO of underwater aperture-cavity, experiments of FIO characteristics and its control of underwater aperture-cavities were carried out in the circulating water tunnel. The experimental model of underwater aperture-cavity was designed based on the surface aperture structure of underwater vehicles, and the FIO control device, leading-edge flow splitter (LFS), was proposed based on the principle of incoming boundary layer diversion. The FIO characteristics of underwater aperture-cavities and the effects of LFS on FIO at different freestream velocities were discussed from the two aspects of the frequency spectrum characteristics and the spatial distribution characteristics of the intracavity pressure fluctuations, while the intracavity pressure fluctuations were measured by the streamwise and spanwise installed dynamic pressure transducers at the bottom of the cavity. The investigation results show that the form of FIO of underwater aperture-cavities is dominated by the self-sustained oscillation of the shear layer, which occurs at a relatively low freestream velocity, such as 2.4 m/s, and has an intensive reinforcement with the increase of the freestream velocity. It was proved that the LFS has a good suppression effect on the FIO of aperture-cavities in water, and the suppression effect is significantly enhanced with the increase of the freestream velocity. Specifically, the maximum suppression of the peak and total level of the intracavity pressure fluctuations spectrum reaches 25.3 dB and 15.6 dB, respectively. Besides, the LFS has a low frequency shift effect on the FIO of aperture-cavities, which is beneficial for avoiding the occurrence of flow-induced cavity resonance. Finally, the spatial distribution characteristics of pressure fluctuations indicate that the suppression mechanism of the FIO of underwater aperture cavities by the LFS mainly lies in destroying the periodic modulation effect of the intracavity flow field.