Underwater radiated noise characteristic of the hydro-spinna tidal turbine under induced cavitation

Over the past decade, the development of marine current turbines has progressed rapidly with prototypes and fullscale devices being deployed in the actual environment. With research focusing on the hydrodynamic and design aspects of the technologies used, little is known of the impact of marine current turbine operation on marine life and the environment. This paper looks at the Underwater Radiated Noise (URN) produced from the operation of the Hydro-Spinna turbine which is a horizontal-axis type concept design under development at Newcastle University. URN measurements were taken from a 280 mm diameter Hydro-Spinna model. The URN measurement was part of a comprehensive investigation conducted on the turbine model, where the local pressure in the tunnel was reduced to induce cavitation to study its characteristics. The noise data was found to correspond to the cavitation observation where the noise increases as more cavitation developed. In addition, only tip vortex cavitation was observed during the investigation indicating that this is the only cavitation characteristic of the Hydro-Spinna turbine. As more tip vortex cavitation was observed, the URN results exhibit an apparent trend, whereby the sound pressure level (SPL) increased and the frequency shifted towards the lower frequency region.