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FP5

NORMA Report Summary

Project ID: G3RD-CT-2001-00393
Funded under: FP5-GROWTH
Country: Italy

Experimental procedure to characterise the spectra of the pressure fluctuations generated by the turbulent boundary layer excitation next to the hull of a vessel

The main source of hydrodynamic noise in a ship is the wall flow around the hull. Turbulent Boundary Layer excitation generates hull vibration through a random moving load (wall pressure fluctuation). As a preliminary step, a simple prototype experiment is performed to investigate the main feature of TBL-excited hydrodynamic noise, which aims at separating it from other noise sources, and understanding the basic correlations between the fundamental quantities involved.

Most literature dealing with measurements of pressure fluctuations on solid surfaces generated by the turbulent boundary layer (usually smooth flat plates), refer to aerodynamic noise excitation. Most experiments were conducted in subsonic wind tunnels. Several models describing the space-time pressure correlation function are provided. In very recent work, these models are used to provide the aerodynamic loads necessary for the vibro-acoustic analysis.

Useful know-how from the experience developed in aeronautics can be exploited, while keeping in mind the main differences between that field and the acoustic TBL excitation in marine applications:
- Presence of the free surface;

- Possible inception of cavitations.

The results obtained from the preliminary experiment show that it is possible to build an experimental procedure that, applied to the ship model, will give general laws for the behaviour of the pressure spectra for a certain class of ship.

Reported by

Istituto Nazionale per Studi ed Esperienze di Architettura Navale
139 Via di Vallerano 139
00128 Rome
Italy
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