Experimental study of bubble sweep-down in wave and current circulating tank: Part II—Bubble clouds characterization

In this second part, images acquired from the specific trials developed in order to study the phenomenon of bubble sweep-down are analysed. A post-processing method has been developed to analyse the two air entrainment mechanisms described in the first part, for several test configurations. Bubble clouds are described in terms of depth, area and velocity for both vortex shedding and breakingwave bubble clouds. A parametric study is also performed to calculate the influence of each test parameter on the frequency of bubble generation. It is demonstrated that the occurrence of bubble clouds is proportional to the wave height, with a considerable influence of the phase shift between waves and motions. The overall results provide new elements for the understanding and the study of the phenomenon, with the final objective of obtaining a reliable tool that facilitates the design of research vessels. The authors gratefully acknowledge the DGA (the French Government Agency for Defense) and Ifremer for the financial support of this co-financed Ph.D. thesis. We also would like to thank Thomas Bacchetti and Jean-Valery Facq for their assistance in the design and set-up of these experiments, and Alcino Ferreira for the proof-reading of the final paper.