Author(s): Indrajith D. Nissanka; Poojitha D. Yapa
Linked Author(s):
Keywords: Droplet breakup; Droplet coalescence; Breaking waves; Oil droplet sizes; Oil spill modeling; Surface oil slick
Abstract: In a surface oil spill, oil entrained into the water column as droplets and their eventual surfacing play an important role in oil dispersion and surface spreading. A surface slick can be dispersed into the water column as small oil droplets predominantly by the surface breaking waves. Wave breaking produces oil droplets of a spectrum of diameters, which are penetrated into different depths in the water column. The droplets in the water column further breakup and coalesce due to water column turbulence. The ability to calculate the oil Droplet Size Distribution (DSD) and its dynamic behavior in the water column are important in oil spill modelling. Despite its importance there are no accurate ways to calculate the DSD and intrusion depth of oil droplets. Most of the available oil spill models only consider the vertical exchange of droplets between the surface slick and the mixing layer or use empirical equations to calculate the oil DSD. In this paper, a phenomenological model is introduced to calculate the oil DSD under breaking wave conditions by considering the droplet breakup and coalescence. The evolution of droplet size distribution is calculated using population balance equation. The droplet breakup and coalescence are considered as birth and death terms of droplet sizes while droplets advect and diffuse in the water column due to ambient currents, droplet buoyant velocities, and water column turbulence. The model is used to simulate a recent set of experiments and the model results show a good agreement with observed data.
Year: 2016