Two medium size cavitation tunnel hydro-acoustic benchmark experiment comparisons as part of a round robin test campaign

Abstract

The increase in marine transportation in the last decades has resulted in a rise of the different emissions linked to it. Amongst various detrimental emissions of shipping activities, underwater noise is known to affect ambient noise levels and hence threaten the life (or even survivability) of marine mammals. This concern brought the underwater radiated noise (URN) to the attention of regulators, considering the possible need to limits for commercial ships, thus resulting in a surge of interest.As being the main contributor to the URN of ships, the accurate prediction of propeller cavitation and hence associated noise in the design stage is crucial for achieving reductions in terms of emitted sound pressure levels. Whilst computational methods are developing at an exponential pace and so are prospective tools for the future, model scale experiments still represent the most reliable and largely adopted approach for the prediction of propeller radiated noise. Despite the importance of model tests, being the only reliable tool for cavitation noise prediction, a benchmark data is non-existent for facilities all over the world to compare and correlate their noise measurements.Within this framework, this paper presents the first comparison of a round robin test campaign amongst the Noise CoP (Community of Practice) of Hydro Testing Forum (HTF). Based on the extensive experiments conducted first at Emerson Cavitation Tunnel (ECT), a reduced test matrix is proposed to the forum members. University of Genoa (UNIGE) is the first member to complete the tests specified in the reduced matrix and this paper presents comparisons between the test results of ECT and UNIGE cavitation tunnel in terms of measured sound pressure levels, propeller open water performance, cavitation observations and cavitation inception characteristics. Moreover, in order to shed a light on the issue of propeller cavitation noise measurements, a series of investigations are carried out by UNIGE scrutinizing the effect of hydrophone position, oxygen content, propeller shaft revolution rate, sensitivity to thrust coefficient and cavitation number.