An experimental investigation on cavitation, noise, and slipstream characteristics of ocean stream turbines

The paper presents an experimental investigation on the cavitation, noise, and slipstream characteristics of an ocean tidal stream turbine together with a discussion on the test facilities and methodology used. The experiments were conducted in a cavitation tunnel used to test marine propellers, with the same similarity laws as are used for a marine propeller. The cavitation patterns were observed at conditions corresponding to pre-stall, stall, and poststall stream speeds as well as for two different depths of submergence of the turbine shaft to simulate the static presence of waves. The noise levels of the turbine were measured at the same conditions as the cavitation tests. The experimental results show that the turbine can experience strong unstable sheet and cloud cavitations as well as strong tip vortex cavitation at a shallow depth of shaft submergence which can be imposed by a wave trough taking place over the turbine. It is also shown that the measured noise level of the turbine is further increased due to the presence of cavitation. Finally, the slipstream wash was measured in terms of field velocities in the wake and surrounding of the turbine, and results show the slipstream wash may have an impact on the seabed if a turbine is positioned too close to it.