CEE Seminar: Turbulence – a Central Theme to Hydrologic Sciences and Engineering

McDonnell Douglas Engineering Auditorium
Tirtha Banerjee, Ph.D.

Director's Postdoctoral Fellow
Environmental and Earth Sciences Division
Applied Terrestrial, Energy and Atmospheric Modeling (ATEAM)
Los Alamos National Laboratory

Abstract:  The problem of turbulence is an active area of research because of the large and diverse clientele it attracts - including mathematicians, astrophysicists, atmospheric physicists, environmental scientists, hydrologists, ecologists, oceanographers, and aeronautical, mechanical and chemical engineers. All of these natural scientists and engineers have different needs and approach the problem of turbulence with correspondingly different emphases and tools. Moreover, the aspect of resolving turbulent flows is a key component in quantifying the interactions between land/biosphere and atmosphere, which is central to a number of disciplines such as prediction of local and global weather, climate and ecosystems, hydrology, water resource management, and air and water pollution monitoring etc. However, from the perspective of an applied physicist, this vast multitude of seemingly different problems arising in various natural environments can be systematically organized into a study of turbulent flows under different boundary conditions of increasing order of complexity. Hence, it is safe to state that there exists a common need to describe turbulent flow statistics close to interfaces such as solid, vegetated, water, or multiphase boundaries (air-water-vegetated systems). This encapsulates the scope of the presentation. We will start with a simple phenomenological theory that can describe bulk flow properties of environmental and engineering flows bounded by a wall (e.g., pipe flow) from the statistical properties of the turbulent boundary layer. Nevertheless, in natural flows, quantifying the transport of fluxes is further complicated due to the presence of interfaces and coherent structures. Therefore, we will explore a range of numerical models starting from Reynolds-averaged Navier Stokes (RANS) to large eddy simulations (LES), which can provide deeper insights into mass, momentum and energy exchange between complex boundary conditions (e.g., vegetated land surface, topography) and the atmosphere. It is noteworthy that these exchange processes essentially control the cycles of carbon and water. Coupling such turbulence modeling capabilities over land surfaces with active controls on photosynthesis and transpiration exerted by vegetation, we will discuss simulation capabilities of wildfires and other disturbances/resilience in the landscape scale. Provided that surface - atmosphere energy exchange explicitly impacts the hydrological cycle, we will also present experimental and numerical studies of overland flow and flow through aquatic vegetation, important for a range of water resource engineering applications. To conclude, we will discuss future research directions toward creating a comprehensive framework to integrate aspects of active management and resilience development for the sustainability of ecohydrological resources, built around the central theme of turbulence and environmental fluid mechanics.

Bio: Tirtha Banerjee is a distinguished postdoctoral fellow at Los Alamos National Laboratory (LANL) in New Mexico. He grew up in Calcutta, India, where he completed his bachelor’s degree in civil engineering. During his undergraduate studies, he conducted research in the areas of structural dynamics and aerospace engineering in India and Germany as a DAAD (German Academic Exchange Service) Fellow. In 2011, he moved to the U.S. and joined Duke University in Durham, North Carolina, as a Ph.D. student, and conducted theoretical, numerical and experimental studies involving environmental fluid dynamics and turbulent flows. He received his doctorate in 2015 and joined Karlsruhe Institute of Technology (KIT) in Germany for postdoctoral research in atmospheric boundary layer dynamics. He relocated to the U.S. in early 2017 to join LANL and started working on modeling wildfires and ecosystem disturbances as well as exploring new tools such as quantum computing. Apart from research, he also enjoys outreach activities and mentoring students.