Bag-breakup fragmentation as the dominant mechanism of sea-spray production in high winds

Troitskaya, Yuliya; Kandaurov, Alexander; Ermakova, Olga; Kozlov, Dmitry; Sergeev, D. A.; Зилитинкевич, С.

doi:10.1038/s41598-017-01673-9

Cited by 54 publications

(44 citation statements)

References 14 publications

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“…Natural and laboratory observations show that spume drops are typically formed in the vicinity of the wave crests (Andreas et al, ; Fairall et al, ). The latest results of high‐speed video recording in laboratory experiments by Troitskaya et al () and Troitskaya, Druzhinin, et al () testify that the so‐called bag‐breakup fragmentation taking place at the wave crests is mainly responsible for spume drops production. The drops injection above wave crests was also employed in Lagrangian stochastic models (cf.…”

Section: Governing Equations and Numerical Methodsmentioning

confidence: 99%

“…The bag is inflated by the wind and finally bursts and produces hundreds of droplets. Troitskaya et al (2017) and Troitskaya, Druzhinin, et al (2018) developed a statistical description of the bag-breakup phenomena, but the Probability Distribution Function (PDF) of the drops velocities at injection still remains unknown and requires further research.…”

Section: Introductionmentioning

confidence: 99%

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The Study of Momentum, Mass, and Heat Transfer in a Droplet‐Laden Turbulent Airflow Over a Waved Water Surface by Direct Numerical Simulation

2018

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This paper investigates turbulent exchange processes in a droplet‐laden air flow over a waved water surface by performing direct numerical simulation (DNS). Turbulent Couette flow is considered in DNS as a model of a constant‐flux layer in the marine atmospheric surface layer. Two‐dimensional stationary waves at the water surface are prescribed and assumed to be unaffected by the airflow and/or droplets. Evaporating droplets of different sizes are injected into the air in the vicinity of wave crests with initial velocities and temperatures of water, and thus mimicking spume sea‐spray droplets. Evolution equations of the airflow velocity, temperature, and humidity are solved in a Eulerian framework simultaneously with the equations of individual droplets coordinates and velocities, temperatures, and masses tracked in a Lagrangian framework. The momentum (Qm) and sensible (QS) and latent (QL) heat fluxes from the droplets to air are evaluated both as phase‐averaged Eulerian fields and as fluxes integrated over time along Lagrangian droplets trajectories. The results show that droplets extract momentum from the surrounding air (Qm < 0), and QL > 0 and increases with droplet diameter, d, whereas QS < 0, reaches maximum for droplets with diameters of the order of 200 μm, and saturates for larger droplets. The resulting enthalpy flux QS + QL > 0 vanishes for droplets with diameters d < 100 μm, and increases with d for larger droplets. DNS results also show that droplets reduce mean air velocity and temperature and increase relative humidity as compared to the droplet‐free flow.

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Section: Governing Equations and Numerical Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Study of Momentum, Mass, and Heat Transfer in a Droplet‐Laden Turbulent Airflow Over a Waved Water Surface by Direct Numerical Simulation

2018

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“…The dominant contribution to backscatter signal is formed at wave breakers, which overrun the dominant surface waves by definition. The structure of the water surface in the wave breakers is very complex including foam fraction, spray, separated fragments of fluid, and torn from the wave crests by strong wind (see, e.g., Troitskaya et al, ). Due to its complex structure, the wave breakers are expected to have depolarization properties and can contribute to cross‐polarized radar backscatter similarly to the foam layer considered by Fois et al ().…”

Section: Doppler Spectra Analysismentioning

confidence: 99%

“…For constructing parameterization of the dependence of area of the water surface swept by breakers on u * we used the concept of the universal Gibbs method and the Boussinesq analogy between the turbulent velocity fluctuations and the thermal motions of molecules in gas. Previously, we successfully used similar approach for description of the spray‐generating statistics of the bag‐breakup phenomenon closely related to the wave breaking in Troitskaya et al (). The central concept of the Gibbs method is the canonical ensemble or an ensemble of states of a thermodynamic system in weak thermal contact with a heat bath , that is, environment that keeps its temperature unchanged.…”

Section: Verification Of the Backscatter Mechanism And Parameterizatimentioning

confidence: 99%

Cross‐Polarization GMF for High Wind Speed and Surface Stress Retrieval

et al. 2018

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This paper describes the construction of geophysical model function (GMF) for wind speed and surface stress retrieval at high winds from cross‐polarized radar backscatter at the water surface. The starting point is the laboratory experiment designed for the study of X‐band backscattering from water surface. In particular, it was shown that cross‐polarized normalized radar cross section (NRCS) keeps sensitivity to wind friction velocity at high winds alternatively to co‐polarized radar return. Basing on the analysis of the Doppler spectra and simultaneous measurements of parameters of surface waves, we suggest a hypothesis that at high winds the cross‐polarized backscattered signal is formed mainly due to scattering from wave breakers. The hypothesis is supported by the experimentally detected proportionality between the power of the scattered signal at cross polarization and the area swept by wave breakers. These results obtained in the laboratory environment are applied for constructing the similar dependencies for field conditions. Using the phenomenological statistical physics approach, a parameterization of active whitecap coverage fraction dependence on wind friction velocity is suggested. With the use of this parameterization, the empirical function expressing the cross‐polarized NRCS by u* is derived. Using the surface drag parameterization applicable at strong winds, this dependence is verified on the base of available data sets containing collocated satellite measurements of cross‐polarized C‐band NRCS and ground measurements of wind speed. GMFs for u* and U10 retrieval are suggested. Analysis shows that taking into account the angular dependence of cross‐polarized radar backscattered power improves the accuracy of wind speed and wind friction velocity retrieval.

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“…Ortiz-Suslow et al [35,36] discovered that the concentration of spume droplets is proportional to r −3 at high wind speeds. Troitskaya et al [37] pointed out that the breakup of large air pockets near the water surface is the major process that generates sea spray droplets at hurricane wind speeds.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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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.

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Bag-breakup fragmentation as the dominant mechanism of sea-spray production in high winds

Cited by 54 publications

References 14 publications

The Study of Momentum, Mass, and Heat Transfer in a Droplet‐Laden Turbulent Airflow Over a Waved Water Surface by Direct Numerical Simulation

The Study of Momentum, Mass, and Heat Transfer in a Droplet‐Laden Turbulent Airflow Over a Waved Water Surface by Direct Numerical Simulation

Cross‐Polarization GMF for High Wind Speed and Surface Stress Retrieval

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

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