Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session H11: Geophysical Fluid Dynamics: Air-Sea Interaction (5:45pm - 6:30pm CST)Interactive On Demand
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H11.00001: Numerical resolution of bubble and droplet size distributions in breaking ocean waves Wouter Mostert, Stephane Popinet, Luc Deike We present high-resolution direct numerical simulations of three-dimensional breaking ocean waves using the two-phase Navier-Stokes equations with surface tension. We use adaptive mesh refinement, here capable of attaining resolutions equivalent to ${2048}^{3}$ cells in conventional grids, and which resolves physics of the bubble and droplet generation and breakup resulting from the wave breaking process. The bubble statistics are thus well-resolved below the Hinze scale (at which surface tension resists the deforming action of turbulent shear), showing good agreement with experiment. The droplet statistics are the most challenging to resolve numerically, and show a strong dependence on Bond number (comparing surface tension to buoyancy effects), but also show good agreement with experiment. In particular, certain aspects of the droplet distributions are reproduced similarly to recent experiment despite differences in wave initialization. Finally, we discuss numerical considerations on resolution constraints for bubble and droplet statistics. [Preview Abstract] |
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H11.00002: Spray Generation by Collective Bubbles Bursting Baptiste Neel, Luc Deike The bursting of surface bubbles, understood as a production mechanism of sea spray aerosols, is a key feature of mass transfer between ocean and atmosphere. While recent progress has been made to understand the role of water physico-chemistry on the aerosols, experimental works linking collective effects on the bubbles assembly to the spray production remain elusive. Our study, based on a laboratory controlled bubble plume, characterizes directly different surface bubbles collective behaviors, as well as the related spray production. We highlight the role of surface-active material on the surface bubbles and the consequences for the spray. [Preview Abstract] |
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H11.00003: The Dynamics of Plunging Breakers and the Generation of Spray Droplets Martin Erinin, Sophie Wang, Benjamin Schaefer, Xinan Liu, James Duncan The breaking dynamics and spray generation by plunging breaking waves is studied in laboratory-scale experiments. Weak, moderate, and strong plunging breakers are mechanically generated using a dispersively focused wave packet technique. The spatio-temporal evolution of the breaker profile is measured at the center plane of the tank using a laser-induced fluorescence technique capturing ten realizations for each of the three breakers and covering a measurement region one wavelength. Phase averaged mean breaker profiles are computed and are used to characterize the three breakers based on geometric features like the jet impact speed and spatio-temporal distribution of surface roughness. Mean breaker features are found to be highly repeatable throughout the non-linear breaking process. Droplet positions, velocities, and radii (d $\geq$ 100 $\mu$m) are measured for the same three breakers using a cinematic digital in-line holographic system positioned at many streamwise measurement positions located 1 cm above the maximum wave crest height. Droplet generation mechanisms are correlated to mean breaker characteristics. [Preview Abstract] |
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H11.00004: A sea-state dependent gas transfer formulation Sheetal Ramsurrun, Brandon Reichl, Leonel Romero, Luc Deike While classic gas transfer parameterizations used in Earth system models are exclusively dependent on wind speed, the local sea-state is a direct driver of air entrainment and bubble production, which modulates exchange of gases between the ocean and the atmosphere. We combine the gas transfer formulation from previous work (Deike \& Melville, 2018), that accounts for wind, wave parameters and a bubble mediated gas flux model, and use recent progress in wave modeling (Romero, 2019) to directly compute the breaking statistics within WAVEWATCHIII. We investigate the role of the full wave complexity at high temporal and spatial resolution on the gas flux, capturing the wave field associated with storms with a high level of fidelity, and opening a pathway for more accurate models of ocean-atmosphere interaction, from gas transfer to spray generation, based on the present formulation. We will compare our modeling approach to data sets for various gases, key to the climate system, in particular DMS and CO$_{2}$. (Brumer et al., 2017; Bell et al., 2017). [Preview Abstract] |
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H11.00005: Enabling explicit wave-atmosphere coupling in the Weather Research and Forecasting model using immersed boundary methods Zhao Wu, Jeffrey D. Mirocha, Robert S. Arthur, David J. Wiersema, Katherine A. Lundquist, Peiyun Zhu, Oliver B. Fringer Immersed boundary methods (IBMs), implemented into the Weather Research and Forecasting (WRF) atmospheric model for complex terrain and urban applications, have been extended to represent moving objects, such as sand dunes or water waves. Validation of the moving IBM implementation is presented, comparing the impacts of moving cylinders, hills and waves on the flow against published experimental and simulation results. Comparisons are also made to simulations using WRF’s native terrain-following grid, and stationary WRF-IBMs (Lundquist et al. 2012; Bao et al. 2018; Wiersema et al. 2020; Arthur et al. 2020). Sensitivities to different IBM formulations, including velocity and shear stress reconstruction approaches, as well as the type of wave boundary condition, are also presented. Utilization of moving IBMs in atmospheric large-eddy simulations to support offshore wind energy application is also discussed, including coupling with a prognostic wave model to provide realistic evolving wave height and velocity information. [Preview Abstract] |
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H11.00006: Wind/Aerosol LiDAR measurements at a coastal zone Yajat Pandya, Meng Li, Di Yang, Giacomo Valerio Iungo Production and transport of the marine aerosol in the Marine Atmospheric Boundary Layer (MABL) flow depend on several factors including wind speed, shear, turbulence intensity, wave height, steepness, and wave age. The coastal zone of the MABL flow undergoes complex processes of wave breaking and wave crashing that significantly differ from the aerodynamically smooth conditions typical for the open ocean. Using ground-based measurements of wind speed and aerosol backscatter from a pulsed Doppler wind LiDAR, it is possible to characterize the spatio-temporal distribution of marine aerosol under different wind directions. Fixed LiDAR scans were performed at the Galveston Island State Park, TX, which have enabled estimating friction velocity and aerodynamic roughness length for different wind/wave/atmospheric conditions. We compare these flow parameters with the equivalent values typically predicted through an open- ocean model (Andreas \textit{et al}., 2012) to single out differences of orders of magnitude in aerodynamic roughness length, which are connected with wave breaking, spraying and foam owing the coastal zone. Finally, an empirical model to predict aerodynamic roughness length from the friction velocity for coastal zone is proposed. [Preview Abstract] |
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H11.00007: Turbulent Transport of Spray Droplets Near Realistic Multispectral Surface Waves Kyle Rocha-Brownell, Robert Jaquette, Fabrice Veron, David Richter Functions governing the generation of spray and aerosols at the sea surface are often estimated using the so-called flux profile method, which requires only fixed-height concentration measurements. The simplest form of this method assumes a balance between spray emission and deposition, resulting in a simplistic power-law for vertical concentration profiles. The focus of this joint experimental-computational project is to evaluate the effect of multispectral waves on this power-law theory over a range of sea spray droplet sizes. Large-eddy simulations with inertial Lagrangian particles are used to resolve the turbulent transport of spray droplets around real multispectral wave data obtained from the University of Delaware Air-Sea Interaction Laboratory. During the simulation, concentration measurements are taken over this dynamic bottom boundary. For each case, the resulting concentration profiles are compared with that of the flux profile method. Agreement and discrepancies with the power-law theory, particularly as resulting from the finite inertia of the droplets, are discussed. [Preview Abstract] |
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H11.00008: The Sensitivity of Spume Droplet Trajectories to Initial Conditions Robert Jaquette, Fabrice Veron Marine aerosols (sea spray) facilitates the exchange of momentum, heat, and moisture across the air sea interface. Quantifying the total exchange between spray and the surrounding atmosphere remains critical to our further understanding of topics such as climate change and tropical cyclone intensification. However, estimating the total spray-induced air-sea fluxes from inertial droplets remains difficult due to a lack of observations associated with the generation (i.e. fluxes) of drops at the air-sea interface. In this work, we utilize a Lagrangian stochastic model based upon coupled dynamic and thermodynamic equations, to generate sets of single drop trajectories, as well as radii, temperatures time series. In this talk, we present results on drop lifetimes and vertical distributions under various initial atmospheric/wave conditions. The results suggest a strong sensitivity to initial conditions for droplet ejection, particularly for spume droplets, which are subsequently exposed to different regions within the wave boundary layer thereby influencing the ultimate thermodynamic drop-atmosphere transfers. These results suggest that experimental work is needed to improve our understanding of the mechanism of spume generation. [Preview Abstract] |
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H11.00009: A study of the ocean spray effect on the vertical transport of momentum with a multi-fluid-type model under high-wind conditions of a hurricane Yevgenii Rastigejev, Sergey A. Suslov In the present work we have developed an Eulerian multi-fluid-type mathematical model to describe a marine atmospheric boundary layer (MABL) laden with ocean spray. The model employs a multi-phase variable density E-epsilon turbulence closure and considers spray as a continuous medium interacting with the gas phase. The ensemble averaged conservation equations for mass, momentum and turbulent kinetic energy are formulated separately for the gas and liquid phases. The multi-fluid approach allows us to describe turbulent air-spray interaction consistently and accurately in contrast to previously used mixture-type models. Particularly, this approach enables us to account for the influence of the droplets on the turbulence intensity in the gaseous phase due to inter-facial momentum transfer in addition to the gravitational suppression of the turbulent intensity by the spray. The numerical and asymptotic analysis of the MABL with the new multi-fluid model demonstrate that the model predicts significantly different vertical distributions of spray density and characteristics of the turbulent flow especially for intermediate and large droplets compared with more conventional mixture-type models. [Preview Abstract] |
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