Hull induced noise. Part 1: Hydrodynamic noise produced by the turbulent flow around a rigid hull

Authors:

  • Fureby Christer
  • Almström Henrik

Publish date: 2001-01-01

Report number: FOI-R--0130--SE

Pages: 23

Written in: English

Abstract

Surface ships, submarines and other submersibles all have a hydroacoustic signature that is revealing for passive sonar in stationary and mobile surveillance systems, and may also interfere with the ship´s own sonar. The sources of the hydroacoustic signature can be divided into internal and external sources. The internal sources mainly consist of onboard machinery whilst the external sources mainly consist of the hydrodynamic noise, i.e. the sound from the turbulent boundary layer. The internal sources depend on the operating conditions and the tactical situation, and advanced signature reduction has been used for a long time. As regards the external sources not much has been done due to the lack of knowledge about the fluid dynamics and the prediction methods. The present study is divided into two parts where part 1 is a contribution towards a better understanding of the fundamental physics of hydrodynamic noise produced by the turbulent flow around a rigid hull, whereas part 2 focuses on hydrodynamic noise produced by a vibrating hull excited by the turbulent flow. A methodology is here developed to predict the sound radiated by a surface ship, a submarine or other underwater vehicles, based on splitting the computation into a viscous incompressible flow simulation model, using Large Eddy Simulations, and a separate acoustic calculation. Such a two-step approach is particularly attractive for a nearly incompressible flow, since a fully compressible simulation of a virtually incompressible flow is both too expensive (since the acoustic time scales need to be properly resolved) and unnecessarily complicated. Finally, we apply this calculation procedure to the flow around a prolate spheroid in order to demonstrate the method. Qualitative or quantitative comparison with experimental data is planned in a future study.

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