Direct and Indirect Experimental Methodologies for the Hydro-Acoustic Analysis of Marine Propellers

The present paper reviews two "unconventional" approaches to experimentally address the diagnostics, analysis and solution of hydroacoustic problems in naval engineering. The first approach, based on direct pressure fluctuation measurements combined with detailed flow measurements in the proximity of the noise source, provides a direct estimate of the flow phenomena at the origin of sound generation and emission. The second approach is a relatively recent strategy to investigate the sources of acoustic noise in the aeronautical field and concerns the use of volumetric techniques, such as Tomographic PIV (Elsinga, et al., 2006), in combination with acoustic analogies. The abilities of the two approaches are investigated with reference to the analysis of the noise sources in some test cases consisting of an isolated propeller, a propeller operating in the wake a surface ship, and an open-water propeller-rudder system. Both approaches are shown to enable the physical interpretation of the potential mechanism of noise generation and emission from a naval propeller.