Planar bubble plumes from an array of nozzles: Measurements and modelling

Abstract

Bubble curtains are widely used for sound mitigation during offshore pile driving to protect marine life. However, the lack of well validated hydrodynamic models is a major factor in the inability to predict the sound attenuation of a bubble curtain a priori. We present a new dataset resulting from bubble curtain measurements carried out in a 10 m deep and 31 m wide freshwater tank. The data describe the evolution of the void fraction profile and the bubble size distribution along the height of the bubble curtain. On this basis, a new relationship is developed for the dependence of the entrainment parameter of the bubble curtain on the air flowrate. In addition, we have extended a recently developed integral model for round bubble plumes to seamlessly capture the transition from initially individual round plumes to a planar plume after their merger. With additional modifications to the entrainment relation, the effective slip velocity and the initial condition for the bubble size distribution, the new model is found to be in good agreement with the data. In particular, the bubble size distribution sufficiently distant from the source is found to be independent of the gas flowrate, both in the data and in the model.