Stably density-stratified shear flows arise widely in geophysical settings. Instabilities of these flows occur on scales that are too small to be directly resolved in numerical simulations of the oceans and atmosphere, yet drive diabatic mixing events that often exert a controlling influence on much larger-scale processes.
Strongly stratified flows are characterized by the emergence of highly anisotropic layer-like structures with much larger horizontal than vertical scales. Owing to their relative horizontal motion, these structures are susceptible to stratified shear instabilities that induce spectrally non-local energy transfers.
To efficiently describe the dynamics of this “layered anisotropic stratified turbulence” regime, a multiple-scales asymptotic analysis of the non-rotating Boussinesq equations is performed. The analysis yields a new scaling for the root-mean-square vertical velocity in stratified turbulence, which is corroborated using data from direct numerical simulations. The resulting asymptotically- reduced equations are used to investigate the mixing efficiency of certain “exact coherent states” (ECS) arising in strongly stratified Kolmogorov ow. The ECS are computed using a new methodology for numerically integrating slow-fast systems that obviates the need to temporally resolve the fast dynamics associated with the stratified shear instabilities.
Greg Chini is professor of mechanical engineering and director of the Integrated Applied Mathematics Ph.D. Program at the University of New Hampshire. He earned his doctorate in aerospace engineering at Cornell University, with a focus on a fluid mechanics and applied mathematics, and has held visiting positions at Nottingham University, Caltech, the Institute for Pure and Applied Mathematics at UCLA, the Isaac Newton Institute for Mathematical Sciences at Cambridge University, and the Kavli Institute for Theoretical Physics at UCSB. In 2016, he was elected to the faculty of the Woods Hole Summer Program in Geophysical Fluid Dynamics.
Prof. Chini’s research centers on the application of nonlinear mathematics and high-fidelity numerical simulations to important environmental, energy, and resource challenges facing society. Specific research themes include self-organization and extreme transport in fluid turbulence, multiscale phenomena in geophysical fluid dynamics and geophysics, and mathematical modeling of energy and resource systems.