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Open AccessArticle

Numerical Study on the Generation and Transport of Spume Droplets in Wind over Breaking Waves

by Shuai Tang 1,2,3, Zixuan Yang 3,4, Caixi Liu 1,2,3, Yu-Hong Dong 1,2,* and Lian Shen 3,4,*
1
Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072, China
2
Shanghai Key Laboratory of Mechanics in Energy Engineering, Shanghai 200072, China
3
Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455, USA
4
St. Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN 55414, USA
*
Authors to whom correspondence should be addressed.
Atmosphere 2017, 8(12), 248; https://doi.org/10.3390/atmos8120248
Received: 31 October 2017 / Revised: 28 November 2017 / Accepted: 7 December 2017 / Published: 12 December 2017
(This article belongs to the Section Biosphere/Hydrosphere/Land - Atmosphere Interactions)
Sea spray droplets play an important role in the momentum, heat and mass transfer in the marine atmospheric boundary layer. We have developed a new direct numerical simulation method to study the generation and transport mechanisms of spume droplets by wind blowing over breaking waves, with the wave breaking process taken into account explicitly. In this new computational framework, the air and water are simulated as a coherent system on fixed Eulerian grid with the density and viscosity varying with the fluid phase. The air-water interface is captured accurately using a coupled level-set and volume-of-fluid method. The trajectories of sea spray droplets are tracked using a Lagrangian particle-tracking method. The generation of droplets is captured by comparing the fluid particle velocity of water and the phase speed of the wave surface. From the simulation data, we obtain for the first time a detailed description of the instantaneous distribution of droplets at different stages of wave breaking. Furthermore, the time histories of the droplet number and its generation and disappearance rates are analyzed. Simulation cases with different parameters are performed to study the effects of wave age and wave steepness. The flow and droplet fields obtained from simulation provided a detailed physical picture of the problem of interest. It is found that plunging breakers generate more droplets than spilling breakers. Droplets are generated near the wave crest at young and intermediate wave ages, but at old wave ages, droplets are generated both near and behind the wave crest. It is also elucidated that the large-scale spanwise vortex induced by the wave plunging event plays an important role in suspending droplets. Our simulation result of the vertical profile of sea spray concentration is consistent with laboratory measurement reported in the literature. View Full-Text
Keywords: spume droplets; wave breaking; direct numerical simulation; Lagrangian particle tracking; coupled level-set and volume-of-fluid method spume droplets; wave breaking; direct numerical simulation; Lagrangian particle tracking; coupled level-set and volume-of-fluid method
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MDPI and ACS Style

Tang, S.; Yang, Z.; Liu, C.; Dong, Y.-H.; Shen, L. Numerical Study on the Generation and Transport of Spume Droplets in Wind over Breaking Waves. Atmosphere 2017, 8, 248.

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