Numerical analysis of the effect of a breaking-vortex baffle around appendage on the submarine flow field and flow noise

Controlling the flow and wake of the appendages is an effective solution to realize noise reduction and improve propulsion. The horseshoe vortex is a special vortex structure generated during the flow process of submarine. A large strength horseshoe vortex will pose a threat to the concealment and safety of the submarine owing to the flow inducing in hull and pulsating pressure. In this paper, the breaking-vortex baffles are added around the sail and fin appendages of a submarine to investigate their effects on flow and noise characteristics. The high-fidelity turbulent flows of the submarine hull with and without baffle around the appendages are obtained by the improved delayed detached eddy simulation (IDDES) with which the flow noise characteristics are predicted by the Ffowcs Williams-Hawkings (FW-H) acoustic analogy method. The prediction approach is verified by a classic flow-noise case, showing good agreement with the experiment. The results show that the breaking-vortex baffle added around the appendage produce small vortices in the opposite direction to the horseshoe vortex. These small vortices interfere with the development process of the horseshoe vortex, enhancing the horseshoe vortex dissipation and weakening its intensity, the maximum intensity is reduced by 54.35%, which reduces the pulsating pressure intensity of the wake field and finally achieving the purpose of flow noise reduction, with a maximum noise reduction of 3.64 dB.