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Numerical Study on Kelvin-Helmholtz Instability and Oil Boom Failure Due to Droplet Entrainment
Z. Zhang, C.-F. An and R. M. Barron

In this paper, a numerical study on Kelvin-Helmholtz (K-H) instability of oil-water interfacial phenomena is presented to explore oil boom failure due to droplet entrainment. The K-H instability is analyzed using a small disturbance theory and simulated using the CFD software, Fluent. The results of theoretical analysis and numerical simulation for K-H instability are consistent with each other over a wide range of oil-water density difference and initial disturbed interface wavelengths. The numerical study includes oil-water interface behavior for three different initial interface disturbance shapes (sinusoidal, step and rectangular) and the viscosity effect, as well as the quantitative effects of the wavelength and relative density difference on the critical velocity of the K-H instability of the oil-water interface. The results show that the initial interface disturbance shapes may only affect the strength of the K-H instability, but has no obvious effect on the value of the critical velocities as long as their wavelengths are the same. On the other hand, viscosity has an obvious effect on the interface instability, since it not only reduces the strength of the instability, but it also increases the critical velocity. Numerical modeling of droplet entrainment based on an experiment by Delvigne is also carried out and the agreement between computational prediction and experimental observation is quite satisfactory. This shows that numerical simulation has the ability to accurately predict K-H instability and oil droplet entrainment in practical flow situations.

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