2025_programme: Cavitation on small craft propellers and its contribution to underwater radiated noise

• Day: June 19, Thursday
    Location / Time: A. TERPSIHORI at 17:20-17:40
• Last minutes changes: -
• Session: 27. Radiated noise from Ships and Surface Platforms
  Organiser(s): N/A
  Chairperson(s): Andreas Grech La Rosa
• Lecture: Cavitation on small craft propellers and its contribution to underwater radiated noise
  Paper ID: 2117
  Author(s): Tom Smith, Andrea Grech La Rosa, Solomon McMorran, Giles Piggott, Joao Gaivota
  Presenter: Tom Smith
  Abstract: Cavitation is a major contributor to underwater radiated noise (URN) from commercial ships but less is known about the dynamics, inception speed, and contribution of cavitation to URN for small vessels. Small vessels often use propellers located very close to the free surface and which turn at high speeds. This means that the cavitation dynamics are likely to be different from those on larger ships. Many small vessels are powered by internal combustion outboard engines, which typically expel exhaust gases through the hub, leading to a bubbly hub vortex.\nIn this work, acoustic data from a series of small boat trials are presented alongside underwater camera footage to show how cavitation develops on small high speed propellers and how it contributes to the acoustic signature.\nThe results show that the cavitation inception speeds are typically 5-7 knots, and this is accompanied by a sharp rise in noise across a broad frequency range. For one vessel, visual footage shows that tip vortex cavitation dominates at low speeds and analysis of the acoustic data of other similar vessels indicates this is common. Using wavelet analysis, the high frequency noise associated with bubble collapse is examined with a particular focus on how this noise scales with speed. This shows that the collapse noise scales differently depending on the type of cavitation from which it originates.\nResults are also presented that provide insights into how the material state of the propeller can influence the cavitation dynamics. Whilst rough and fouled propellers might be assumed to cavitate earlier and hence be louder than their smooth counterparts, it is shown here that this is not always the case. When tip vortex cavitation dominates, small amounts of roughness can actually reduce URN levels by disrupting the formation of the tip vortex.\n
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  This paper is a candidate for the "Prof. John Papadakis award for the best paper presented by a young acoustician(under 40)"
• Corresponding author: Dr Tom Smith
  Affiliation: University College London
  Country: United Kingdom