Experimental investigation of pressure pulses and radiated noise for two alternative designs of the propeller of a high-speed craft

The propellers have been designed in the context of a research project starting from two different rake distributions (forward rake to increase thrust and efficiency, backward rake to reduce cavitation), using different techniques (traditional lifting line / lifting surface and optimization algorithm coupled with a panel code), leading thus to rather different geometries. Propellers have been tested through cavitation tunnel experiments. The activity represents an interesting case study for this kind of measurement in presence of rather large cavitation extensions. The effects of cavitation on different components of pressure pulses and noise are investigated for the different rake distributions adopted. Results clearly shows the effects of this geometrical characteristic on cavitation and pressure pulses pointing out that, in some cases, propeller hydrodynamic performances may determine pressure pulses intensity more than cavitation extensions. A simplified numerical approach, adopting stationary RANS calculations, for the evaluation of the effects of propeller geometry, has been proposed. Results show a good correlation with measurements allowing to have an insight into the phenomenon and confirming the effect of the rake.