Measurements of hydrodynamic noise from submerged hydrofoils

This paper presents the results of an experimental study of hydrodynamic noise conducted in the High-Speed Water Tunnel of the California Institute of Technology. The objective of the test program was to measure some of the basic characteristics of noise radiated from submerged hydrofoils, both fully wetted and cavitating. Measurements of fully wetted hydrodynamic noise are difficult to make due to the low intensities, but the very low background noise level of the Caltech tunnel makes it possible to measure this noise under some conditions. An increase in the angle of attack of a hydrofoil was found to produce a slight increase in noise spectrum level at high frequencies. An increase in surface roughness produced a more significant increase over a wider frequency range. Noise was measured for three distinct types of hydrofoil cavitation: blade surface cavitation, wake cavitation, and trailing vortex cavitation. Foil vibration was found to be important in blade surface cavitation, but not in the other forms. Both blade surface and wake cavitation have spectral peaks at a Strouhal number based on a cavity length of 0.5. Trailing vortex cavitation is found to be a relatively weak source of noise, owing to the fact that in the water tunnel this type of cavitation is gaseous in nature. Subject Classification: [43]30.70, [43]30.85, [43]30.50.