Acoustic noise emission of air turbines for wave energy conversion: Assessment and analysis.

The oscillating-water-column (OWC) system is one of the most developed wave energy conversion technologies, and several prototypes have been deployed and tested on the sea. Noise emission is essential to this technology's long-term environmental impact assessment. The power take-off system of an OWC comprises a self-rectifying air turbine that directly drives an electrical generator. The paper compares the noise emission of a biradial turbine with that of a Wells turbine. The noise emission of the biradial turbine was measured at the Instituto Superior Técnico variable-flow test rig, while the Wells turbine data were collected in the literature. Acoustic measurement procedures followed the guidelines of the ISO 3746 Standard. A definition of specific noise level is used to compare the noise emission from geometrically similar air turbines or other air turbines performing the same duty. The results show that the noise levels of the biradial turbine are significantly lower than those of the Wells turbine at off-design conditions for the same pneumatic power. • Methodology for measuring noise emission from air turbines. • Experimental characterisation of the acoustic emission of a biradial turbine. • Use of a specific noise level to compare air turbines. • Comparison of noise emission of a biradial turbine with a Wells turbine. • Wells turbines are significantly noisier than biradial turbines at off-design conditions. [ABSTRACT FROM AUTHOR]