Objectives  The characteristics and influencing factors of the radiated noise generated by the blowdown of sewage from underwater vehicles is investigated.

  Methods  The flow field analysis and the quantitative calculation of radiated noise of large-diameter air jet were carried out based on Large Eddy Simulation(LES)and FW-H equation calculation method.

  Results  The calculated and experimental results show that the radiated noise is mainly related to the pressure difference between the blowdown pressure and the back pressure, and is basically not affected by the blowdown back pressure. As the pressure difference increases, the radiated noise becomes larger. As the sanitary pressurized tank is blown out, the radiated noise experiences a breakthrough and increases significantly due to air jet under the water. Moreover, the spectrum shows a low frequency characteristic. The radiated noise is mainly concentrated in the range of 0-1 500 Hz and there are significant peaks appears in the spectrum, and there is a significant peak.

  Conclusions  A reasonable measure to weaken the radiated noise during the process of blowdown is to control the pressure difference and prevent the appearing of the high pressure air jet under the sea.