The bubble sweep-down phenomenon around oceanographic research vessels generates acoustic disturbances. A specific experimental protocol in a wave and current circulating tank is used to study this phenomenon around a 1/30 scale ship model in a configuration with current, waves and ship motions. 3D visualizations of the bubble clouds and Stereo-PIV (Particle Image Velocimetry) measurements results, both obtained in the bow vicinity of the ship model, are presented in this paper. The behaviour of the breaking wave with bubble generation is studied and the spatial evolution of the bubble clouds is investigated. It is demonstrated that the bubble cloud generation is mainly conditioned by the ascending vertical velocity of the flow near the bow. It is observed that the bubble clouds are propagated in the flow direction with a horizontal expansion which is non negligeable, reaching a close position to the hull. The overall results provide new elements for the study and the understanding of the phenomenon compared with previous 2D studies. Highlights ► Air entrainment is studied around a 1/30 Scale Ship Model. ► 3D bubble cloud characteristics are determined. ► PIV measurements and POD analysis allow to study the air bubble generation.

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International audienceThe bubble sweep-down phenomenon around the oceanographic research vessels generates acoustic perturbations. A specific experimental protocol has been developed in a wave and circulating tank to study this phenomenon. This protocol is used to carry out trials on three different ship models in order to study the influence of the bow geometry on the bubble generation. For different test configurations, bubble clouds are described and compared in terms of area, maximal depth and vertical velocity to highlight bubble cloud dynamics surrounding the three ship models. The relation between the hydrodynamic flow field and the bubble generation is studied by means of Particle Image Velocimetry (PIV) measurements to study the phenomenon by the use of phase averaged velocity fields. The overall results enable us to characterize the bubble sweep-down phenomenon from the air bubble generation and propagation to the frequency of occurrence and the clouds behaviour

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