Analysis of the effect of vortex reduction structures on submarine tonal noise via frequency-domain method employing thickness noise source

Abstract

In this study, the acoustic effect of unfavorable flow, such as horseshoe vortex (HSV) generated around the appendages, on propeller radiated noise was analyzed. To analyze this, a frequency-domain noise model is developed, which can predict the noise of an underwater propeller placed in a non-uniform wake. To clearly analyze the acoustic effects of HSV around appendages, vortex reduction structures (VRS) are installed at the junctions of a submarine where HSV is generated intensively, and the acoustic effects before and after the installation of the VRS are compared. In a hydrodynamic analysis of submarines, adverse pressure gradients are resolved and the HSV is suppressed after installing the VRS. In a hydroacoustic analysis, directivity and contribution analysis by radius and order are performed. In the directivity analysis, when the VRS are installed, the first blade-passing frequency (BPF) is reduced by 5~12 dB, while the second BPF is reduced by up to 20 dB. Through the contribution analysis involving radius, it was found that installing VRS on the rudder is effective in reducing the first BPF noise. By contrast, in the second BPF, the VRS installed on the sail was more effective in noise reduction than that on the rudder.