Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session A26: Geophysical Fluid Dynamics: Air-Sea Interaction I |
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Chair: Gaetano Sardina, Chalmers University of Technology Room: 251 D |
Sunday, November 24, 2024 8:00AM - 8:13AM |
A26.00001: How the oceans breathe: Field measurements of bubble-mediated gas exchange processes in the Labrador Sea Kee Onn Fong, Craig McNeil, Jun-Hong Liang, David Ho The Labrador Sea in the northwest Atlantic presents conditions that favor the co-existence of deep convection and Langmuir circulations that facilitate deep overturning of gases and bubbles resulting from breaking waves on the air-sea interface. The rates and mechanisms of gas exchange in strongly convective conditions are still poorly known due to the lack of detailed measurements in these conditions and incomplete knowledge of bubble processes in gas transfer. Here we present observational results from the Bubble Exchange in the Labrador Sea (BELS) experiment conducted in December 2023, where air-sea invasion rates of O2/N2 are measured using autonomous underwater vehicles (AUVs) equipped with dissolved gas sensors and gas tension sensors. We also present concurrent measurements of bubbles and currents using forward-looking sonars and acoustic Doppler current profilers (ADCP), which enables novel spatiotemporal imaging of bubble volume fractions, sizes, and distributions, as well as measurements of bubble generation from wave breaking and their interactions with Langmuir circulations and convective turbulence. These data sets are used to estimate bubble-mediated gas transfer rates using 1D and 3D budgeting approaches. The goal is to incorporate the model into a more accurate parametrization of air-sea gas exchange to reduce uncertainties in global climate models. |
Sunday, November 24, 2024 8:13AM - 8:26AM |
A26.00002: Numerical study of bubble transport in breaking waves Umberto Costa Bitencourt, Saswata Basak, Grant B Deane, M. Dale Stokes, Han Liu, Anqing Xuan, Lian Shen Bubble-mediated processes in breaking waves are directly associated with bubble residence time, penetration depth, and overall distance traveled in the water. To accurately model the exchange of momentum, heat, and gas between the atmosphere and oceans, an understanding of the main factors that influence the transport of bubbles in breaking waves is crucial. In this study, we perform high-fidelity direct numerical simulations of breaking waves to investigate the motion of bubbles. The bubbles created by breaking waves are resolved using the coupled level set and volume-of-fluid method. A comprehensive description of the Lagrangian trajectories of bubbles throughout the active breaking phase is obtained by employing the optimal network (ON) algorithm. The insights provided by the simulations and analyzed by the ON algorithm significantly advance our understanding of the complex interactions of bubble-mediated processes in the turbulent ocean environment. |
Sunday, November 24, 2024 8:26AM - 8:39AM |
A26.00003: Studying drop production by collective bubble bursting for various bubble size distributions in laboratory experiments Megan Mazzatenta, Martin Aleksandrov Erinin, Baptiste Neel, Luc Deike Bubbles entrained by breaking waves rise to the ocean surface, where they cluster before bursting and releasing droplets into the atmosphere. The ejected aerosols affect cloud formation and the radiative balance of the atmosphere, motivating a controlled study of drop production by collective bubble bursting through a laboratory-scale experiment. Using a 50x50x60 cm3 bubbling tank filled with solutions of artificial seawater, we make measurements of bulk bubbles, surface bubbles, drops, and dry particles for cases with a variety of initial bubble size distributions. As the bubble size distribution is changed, we analyze the corresponding change in the drop size distribution and attribute ejected drops of sizes 0.05-500 microns to associated bursting bubbles spanning 0.03-5 millimeters. We demonstrate that the measured drop production by collective bubble bursting can be described relatively well by the drop size distribution obtained by integrating scaling laws developed for single bubble bursting over the various bubble sizes measured in our experiments. |
Sunday, November 24, 2024 8:39AM - 8:52AM |
A26.00004: Direct Numerical Simulation of Droplets Interacting with Free Surface Han-Hsiang Kuo, Xuanting Hao Droplet interaction with free surfaces is extensively studied due to its relevance in understanding phenomena such as ocean surface salinity distributions, liquid aeration, and capillary waves. Capturing the hydrodynamics associated with multiple droplets poses challenges due to the stochastic nature of droplets. This study addresses these challenges through numerical investigation, focusing on how the vertical and horizontal distances between water droplets affect their interaction with a free surface immediately after impact. We conduct direct numerical simulations using the volume-of-fluid method to characterize the shape and position of fluid interfaces. Adaptive mesh refinement is used to reduce the computational cost needed for resolving detailed flow field dynamics. Our result is validated against previous experimental and numerical studies of droplet impact on liquid pools. In our simulations, droplets are placed close to the free surface, each initially set with a terminal velocity. We gather and visualize data from various combinations of horizontal and vertical distances between the droplets to elucidate post-impact droplet dynamics, including cavity propagation and crown development. |
Sunday, November 24, 2024 8:52AM - 9:05AM |
A26.00005: Wave and turbulent stress transport equations for flow over surface waves Ali Bizhan Pour, Fabrice Veron, Kianoosh Yousefi Understanding air-sea interactions is crucial for both improving weather and climate predictions and has significant implications for marine renewable energies. In the study of turbulent flows over surface waves, the necessity of decoupling the wave-induced and turbulence motion has long been recognized and commonly employed in theoretical and numerical studies. Despite developing the decomposed wave and turbulent conservation equations for mass, momentum, and energy, the further step of looking into the transport equations of wave and turbulent stress is rarely taken. This has prevented the complete resolution of the governing equations and the associated closure problem. |
Sunday, November 24, 2024 9:05AM - 9:18AM |
A26.00006: Generation of waves on a free surface by quadratic shear currents Harishankar K Muppirala, Ramana Patibandla, Anubhab Roy
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Sunday, November 24, 2024 9:18AM - 9:31AM |
A26.00007: A turbulent curvilinear model for wave-induced airflow perturbations for marine atmospheric boundary layer Ghanesh Narasimhan, Georgios Deskos, Ziyan Ren, Lian Shen Progressive waves on the ocean surface influence the structure and turbulence characteristics of the marine atmospheric boundary layer (MABL) flow through wave-induced momentum transfer. This study develops a novel model to predict wave-induced airflow perturbations above surface waves. We extend the linearized viscous curvilinear model from Cao, Deng & Shen (J. Fluid Mech., vol. 901, 2020, A27) by incorporating turbulent stress terms modeled using the Boussinesq eddy viscosity hypothesis. The resulting model equation resembles an Orr-Sommerfeld-like ordinary differential equation with additional eddy viscosity and forcing terms. We conduct large-eddy simulations of wind over progressive waves for various wind-following and wind-opposing wave scenarios, considering different wave ages. These simulations reveal that eddy viscosity in the turbulence-dominated region within the wave boundary layer can be parameterized as a linear function of the vertical distance from the water surface in a wave-fitted curvilinear coordinate system. Our findings demonstrate that solving the turbulent curvilinear model equations enhances predictions of wave-induced fluctuations compared to the linearized viscous curvilinear model, across different wave scenarios. |
Sunday, November 24, 2024 9:31AM - 9:44AM |
A26.00008: Numerical Modeling of Insoluble Surfactants in Two-Phase Flows and Its Application to Breaking Waves Sai Chaitanya Gembali, Lian Shen Surfactants at fluid interfaces significantly impact fluid dynamics by altering the distribution of surface tension. This study models these effects by incorporating Marangoni forces into an incompressible two-phase Navier-Stokes solver. We employ a two-way coupled direct numerical simulation of the two phases, integrating an insoluble surfactant transport equation at the interface. Surface tension is represented using a linear Langmuir isotherm, which linearly relates to local interfacial surfactant concentration. Our framework confines surfactants to the liquid-gas interface, preventing numerical diffusion into the bulk liquid phases. The solver is validated for mass conservation and surface transport against both analytical and numerical solutions. We investigated the effect of surfactants on rising bubbles in quiescent air. The rise velocity of surfactant-laden bubbles decreased compared to clean bubbles, and the terminal bubble shapes were altered due to the formation of stagnation caps. Our observations are consistent with existing research. Furthermore, we examined surfactant effects on breaking waves, focusing on jet profiles and entrainment characteristics in comparison to clean water scenarios. This study can be further extended to analyze surfactant effects on various flow configurations, such as droplet deformation and breakup, as well as the behavior of falling liquid films. |
Sunday, November 24, 2024 9:44AM - 9:57AM |
A26.00009: Salinity and Surfactant Effects on Bubble Bursting in Decaying Rafts Samuel Koblensky, Megan Mazzatenta, Martin Aleksandrov Erinin, Luc Deike Breaking ocean waves generate rafts of bubbles on a large scale, which then burst and produce sea spray droplets which enter the atmosphere. These droplets carry with them aerosols and pollutants which affect the global environment. To understand how ocean conditions affect bursting and sea spray production, we study bubble rafts in artificial sea water with added surfactant. Rafts with standardized size distributions are generated by an impinging jet across varying salinity and humidity conditions. The decay of the rafts is observed synchronously with in-line holographic measurements of ejected droplets. We evaluate the statistical raft decay and drop production through size-dependent bursting and coalescence rates, and ejected droplet size distributions. We will discuss bubble lifetime and droplet production as a function of their sizes and the solution properties, i.e. salt and surfactant type and concentration. |
Sunday, November 24, 2024 9:57AM - 10:10AM |
A26.00010: Dependence of the Transfer Velocity of Carbon Dioxide on the Salt and Surfactant Concentrations in Waterbodies Shivam Verma, Ketan Jawney, Islam Benouaguef, Ian S Fischer, Pushpendra Singh The exchange of gases, such as carbon dioxide (CO2) and oxygen, across the air-water interface is essential to supporting biogeochemical processes that occur in water bodies. In this experimental study, we investigate the dependence of the flux of CO2 on the salt and surfactant concentrations of the water body. The results are described using the stagnant film model in which the gas flux is defined in terms of the transfer velocity and the difference in the gas concentration between the atmosphere and the water body. The model assumes that away from the interface, the water and air are well mixed, and the transport within the film occurs by diffusion. The thickness of the stagnant film depends on the state of mixing in the water body. The state of mixing in our experiments is varied by changing the speed of a magnetic stirrer. The dependence of the transfer velocity on the salt and surfactant concentrations is investigated. |
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