Experimental Investigation of Droplet Generation by Post-Breaking Plunger Waves

Abstract

Understanding the droplet cloud and spray dynamics is important for the study of the ocean surface and marine boundary layer. The role that the wave energy and the type of wave breaking play in the resulting distribution and dynamics of droplets are yet to be understood. The aim of this work was to generate violent plunging breakers in the laboratory and analyze the spray production post-breaking, i.e. after the crest of the wave impacts in the free surface. The droplet sizes and their dynamics were measured with imaging techniques and the effect of different wind speeds on the droplet production was also considered. It was found that the mean radius increases with the wave energy content and the number of large droplets (radius > 1 mm) in the vertical direction increases with the presence of wind. Furthermore, the normalized distribution of droplet sizes is consistent with the distribution of ligament-mediated spray formation. Also, indications of turbulence affecting the droplet dynamics at wind speeds of 5 m/s were found. The amount of large droplets (radius > 1 mm) found in this work was larger than reported in field studies.

Plunging breakers. Part 2. Droplet generation

“…The curves are a bit noisy but generally indicate an increasing droplet number with increasing breaker strength at diameters above approximately 400 µm, the curves converge at smaller diameters. A number of authors have measured droplet diameter distributions in breaking wave and wind wave systems in the laboratory (see for example Veron et al 2012;Ortiz-Suslow et al 2016;Erinin et al 2022;Ramirez de la Torre et al 2022), the field (Wu et al 1984;Monahan 1968) and in DNSs with and without wind (Wang et al 2016;Tang et al 2017;Mostert et al 2022). Many of the distributions in these studies are either fitted or compared with separate power-law functions at small and large droplet diameter ranges.…”

“…of Ramirez de laTorre et al (2022) are reproduced by taking the value of the average droplet diameter as D e = 1.75 mm. The data from the high resolution case in figure13ofWang et al (2016) are reproduced directly.…”

Speed and Acceleration of Droplets Generated by Breaking Wind‐Forced Waves

“…To the best of our knowledge, there is very limited data on acceleration statistics from droplets generated by breaking waves with Ramirez de la Torre et al. (2022) reporting acceleration measurements in wind speeds up to 5 m/s for fairly large drops. Many previous papers have focused on studying the acceleration of inertial and passive particles both experimentally and numerically in homogeneous isotropic turbulence (henceforth referred to as HIT) and boundary layers; see for example, La Porta et al.…”

“…More recently, Ramirez de la Torre et al. (2022) experimentally studied drop speeds and accelerations for mechanically and wind generated breaking waves. A number of laboratory and numerical experiments have investigated the motion of passive and inertial particles in canonical flows such as homogeneous isotropic turbulence (Aliseda et al., 2002; Huck et al., 2018; Ireland et al., 2016; La Porta et al., 2001; Mora et al., 2021; Obligado et al., 2020; Pujara et al., 2019; Sumbekova et al., 2017; Variano & Cowen, 2013) and boundary layers (Berk & Coletti, 2020; Stelzenmuller et al., 2017).…”

“…Of the few studies that have measured droplet dynamics in wind-generated wave experiments, Koga (1981) and Koga (1984) measured the vertical distribution and velocity of large droplets (d > 810 μm) produced by breaking waves and found that the horizontal droplet movement is primarily determined by the wind, while vertical movement is determined by gravity. More recently, Ramirez de la Torre et al (2022) experimentally studied drop speeds and accelerations for mechanically and wind generated breaking waves. A number of laboratory and numerical experiments have investigated the motion of passive and inertial particles in canonical flows such as homogeneous isotropic turbulence (Aliseda et al, 2002;Huck et al, 2018;Ireland et al, 2016;La Porta et al, 2001;Mora et al, 2021;Obligado et al, 2020;Pujara et al, 2019;Sumbekova et al, 2017;Variano & Cowen, 2013) and boundary layers (Berk & Coletti, 2020;Stelzenmuller et al, 2017).…”