Special Seminar: The Role of Instability in Natural and Engineering Fluid Systems
- Wednesday, April 29, 2015 at 4:00pm
- Roberts Hall - view map
Abstract The physical processes at the center of this work are two diﬀerent, yet related, instabilities. The ﬁrst, Rayleigh-Taylor instability (RTI), occurs when a light ﬂuid is underneath, and thus supports, a heavier ﬂuid in the presence of gravity. Vorticity is generated at the interface as small perturbations are exaggerated in time, and the system seeks to reduce the combined potential energy of the two ﬂuids. RTI is observed in a wide range of astrophysical and atmospheric ﬂows and has drastic eﬀects on many engineering systems of interest, such as inertial conﬁnement fusion. The majority of the systems where RTI naturally occurs involve strong compressibility eﬀects. An investigation of compressible RTI using direct numerical simulations requires eﬃcient and eﬀective numerical methodologies, including a wavelet-based adaptive grid, consistent initialization of the system, and non-reﬂecting boundary conditions for strongly stratiﬁed ﬂows. The comprehensive computational framework is used to simulate single-mode compressible RTI for a wide range of compressibility and variable density eﬀects. Similar to RTI, baroclinic instability (BI) involves the generation of vorticity due to the misalignment of pressure and density gradients. In the oceans, BI drives mesoscale (∼ 100 km) eddies, which convert potential energy into kinetic energy by reducing isopycnal (surfaces of constant density) slopes. Mesoscale eddies play a large role in the transport of tracers, which then eﬀects the general circulation through changes in the large-scale distribution of heat and salinity. However, climate models are limited to resolutions too coarse to resolve mesoscale eddies. Thus, the eﬀects of mesoscale eddies are included using a parameterization that diﬀuses along and ﬂattens isopycnals. The focus of this work is to extend the parametrization for anisotropic diﬀusive processes, such as shear dispersion, which results in improved biogeochemical tracer ventilation and a reduction in temperature and salinity biases.
Biography Scott Reckinger earned his Ph.D. in mechanical engineering from the University of Colorado Boulder. He is currently a Postdoctoral Research Associate in the Earth, Environmental, and Planetary Sciences Department at Brown University. Dr. Reckinger’s research interests are in computational ﬂuid dynamics, turbulence, and climate modeling. The focus of his work is the development of accurate and eﬀective numerical methodologies in order to thoroughly investigate the physical processes that aﬀect buoyancy related ﬂuid systems, from idealized hydrodynamic instabilities and the associated turbulent mixing, to the Earth’s oceans and climate system. In addition to collaborations with scientists at the National Center for Atmospheric Research and Los Alamos National Laboratory, Dr. Reckinger has also assisted with undergraduate research and design projects at Fairﬁeld University. He has experience teaching a variety of courses from introductory programming and classical physics, to upper-level ﬂuid mechanics and computational ﬂuid dynamics.