Measurements and modelling of the hydrodynamical and acoustical properties of planar bubble curtains*

The noise emission during pile driving during the construction of offshore installations such as wind farms is harmful to sea life and needs to be mitigated. The usage of bubble curtains is a proven and widely employed solution for this purpose. However, open questions remain e.g. with regard to the relevant noise reduction mechanisms and the reliability of predictions of the system. To tackle these, we developed a novel measurement system for the bubble properties along with acoustical measurements. Our approach is based on electrical, contact-based needle sensors in combination with an optical system. The system is employed to study planar bubble plumes evolving from different nozzle types. All cases display consistent self-similar behavior with spreading rates increasing with increasing gas flow rate, but also varying for different nozzle configurations. We show that such variations critically affect the outcome of available hydrodynamical models for planar bubble plumes. Moreover, we propose a hydrodynamical model which describes our data well and which can be used to predict plume properties in practice. Coupling these results to existing acoustical models, our data allows us to critically assess bubble curtain performance.