Project Overview: The exchanges of mass, momentum, energy, and heat between the atmosphere and the ocean are strongly contingent on small- and large-scale dynamics at the water interface. These air-sea exchanges significantly impact weather phenomena, such as the formation and intensification of storms, as well as long-term climate variability and change. Despite their importance and direct impact on different aspects of human life, many aspects of air-sea interactions remain poorly understood. Surface waves and the accompanying generation of turbulence, airflow separation, breaking waves, spray, bubbles, and plumes play an integral role in coupling the air and sea and forging a strong link between winds, waves, and currents. In this project, we mainly focus on quantifying and parameterizing the effects of these processes on air-sea flux transfers using a combination of experimental and computational/theoretical techniques.

We are particularly interested in characterizing air-sea interaction processes and investigating the role of turbulent processes, surface waves, and oceanic currents in mediating these interactions. Assessing the role of air-sea interactions in extreme weather events is another direction our group is focused on. We investigate the contribution of air-sea interactions to the development and intensification of extreme weather phenomena, such as tropical cyclones, extra-tropical storms, and monsoons. Analyze the influence of oceanic processes on storm tracks, rainfall patterns, and storm surge dynamics. The end goal is to improve weather and climate predictions by utilizing laboratory/field measurements to enhance the representation of air-sea interactions in weather forecast models and climate prediction systems and develop parameterizations and improve model parameter settings to accurately capture the influence of these interactions on regional and global scales.

Here, using controlled laboratory experiments, we investigate the flow structures on both sides of a wind-driven air-water interface and investigate the kinematics and dynamics of the turbulence and coherent structure above and below ocean surface waves. This work also focuses on the early stages of the laminar-turbulent transition of the wind-driven air-sea interface and, in general, wind-wave generation and growth processes. This research leads to a more fundamental understanding of the role of short gravity and gravity-capillary surface waves and the corresponding generation of turbulence and Langmuir circulations in air-sea fluxes.

Project Overview: The integration of renewable energy sources, particularly offshore wind power, plays a pivotal role in mitigating climate change and reducing reliance on fossil fuels. Marine wind energy has grown significantly in recent years due to its vast potential and advantages over its onshore counterpart. However, the presence of surface waves and currents in offshore environments significantly impacts the performance and structural integrity of offshore wind turbines (OWTs) and poses considerable challenges to their design and operation. In particular, surface waves induce dynamic loads that lead to fatigue damage, affect power generation efficiency, and compromise the structural resistance of OWTs. Therefore, understanding the interactions between offshore wind turbines and ocean waves is crucial for optimizing their performance and ensuring long-term sustainability.

Here at the FDT lab, we aim to explore the interaction between OWTs (and other offshore renewable energy systems) and surface waves/currents, to enhance the design and performance of these renewable energy systems. To that end, we explore and characterize the surface wave dynamics (focusing on their generation, propagation, and interaction with OWTs), investigate the impact of wave-induced loads on the structural integrity and fatigue life of wind turbine components subjected to various wind-wave conditions, optimize wind turbine design, and evaluate power generation efficiency. This effort is particularly multidisciplinary, and we collaborate closely with our colleagues at the Mechanical Engineering Department and the Wind Energy Center at UTD (UTD Wind).

Project Overview: Hurricanes account for a significant portion of damage, injury, and loss of life that is attributed to natural hazards and are the costliest natural catastrophes in the US. To date, considerable uncertainties remain on the air-sea interaction processes under hurricane wind conditions, affecting wind loads on off-shore and on-shore structures. These uncertainties partially stem from limitations of both field measurements and/or laboratory experiments and numerical simulations that are incapable of providing a complete picture of the three-dimensional turbulent flow fields. In addition, the current understanding of air-sea interaction processes, even in low to moderate wind conditions, is rather inadequate.

In this project, the recently developed direct numerical and large-eddy simulation frameworks (in the Environmental Flow Physics Laboratory of Columbia University) are combined with field and laboratory measurements to examine the turbulence structure and further elucidate the fundamental mechanisms responsible for air-sea exchanges (i.e., mass, momentum, energy, heat, and moisture transfers) in hurricane boundary layer flows. The results from this research will provide significant insights into the small-scale dynamics of hurricanes and contribute to a wide range of applications, spanning from urban resilience to climate change. 

Funding: National Science Foundation (NSF) sub-awarded through Computing Research Association (CRA), CIF2020-CU-64.

Project Overview: Surface wave breaking is a complicated two-phase flow phenomenon that plays an integral role in coupling the atmosphere and the ocean through generating wave-breaking-induced turbulence, entraining air bubbles into the ocean, and ejecting sea spray into the atmosphere. These small-scale processes largely influence the air-sea exchanges of mass, momentum, and energy across the water interface. The air-sea fluxes are, in turn, affect large-scale weather patterns, sea-state, and climate, and are fundamental components of oceanic and atmospheric models. Therefore, quantifying these exchanges is necessary for improving our understanding of weather and climate systems.

In this project, the details of wave breaking dynamics are explored through direct numerical simulations (DNS) of incompressible Navier–Stokes equations (with surface tension) for two-phase air-water flow. Specifically, the geometric and kinematic breaking criteria, including the steepness associated with incipient wave breaking, the crest-front steepness, the horizontal crest particle velocity, the wave phase speed, and the wave-energy growth rate, are thoroughly examined. Moreover, the onset of wave breaking as a function of Reynolds number and initial wave steepness is also determined at a relatively high Bond number, and a phase diagram in terms of (Re, ε) is introduced to distinguish between breaking and non-breaking gravity waves. Furthermore, the modulation instability of nonlinear Stokes waves and the resulting breaking dynamics is investigated. DNS simulations are performed using an open-source, tree-based adaptative flow solver, Basilisk. The Basilisk solver has been extensively validated for multiphase flows with complex interfacial geometries in particular through comparisons with wave-like solutions for capillary waves and shear-layer instabilities.

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