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Spray Droplet Generation in Breaking Water Waves
Duncan, James H
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This thesis presents the results of an experiment in which the generation of spray droplets in two mechanically generated plunging breaking water waves was investigated. In both breaking waves, the wind velocity at the free surface was zero and droplets were produced only by means of plunging jet impact, free surface turbulence and bubble bursting. The free surface was kept free of particulates and surfactants for each wave in one set of measurements, while in a second set of experiments, using only the higher amplitude wave, the tank water was mixed with a soluble surfactant. The experiment was able to deliver information on the diameter distributions of droplets produced in both waves. Also, the positional and time dependence of droplet production throughout the stages of wave breaking was investigated. Ultimately, it was determined that under these conditions droplet frequency is influenced primarily the impact of the plunging jet with the front face of the wave. Higher amplitude waves generally lead to markedly higher amounts of droplets produced and a shift towards higher diameters. The addition of surfactant reduced the diameter and suppressed the production of spray droplets. The positional distribution of droplet production within the wave was also altered significantly by the presence of surfactant: droplets were more evenly produced throughout the breaking zone in the wave with surfactant, whereas the wave generated in clean water had a much smaller region of significant droplet production.