The Non-Normality of Nature: Intermittency in Turbulent Flows

Abstract 
Nature has a tendency to favor non-normal (or non-Gaussian) distributions. The cosmic microwave background, financial markets, the weather, manufacturing processes and many other phenomena are characterized by such distributions. Here we provide a broad outline of the importance and properties of non-normal distributions and introduce the concept of intermittency, which allows departures from normality to be quantified. We then focus in particular on intermittency in turbulent flows. Intermittency is a major distinguishing feature of turbulence and is intrinsically connected to the nonlinear processes that create enormous spatial and temporal complexity in turbulent flows. We talk about how intermittency affects the dissipation of energy in all turbulent flows and then extend the discussion to intermittency in turbulent reacting flows. Characterizing intermittency in reacting flows is important for developing a better understanding of - and, ultimately, better models for - the interactions between turbulence and flames. Using numerical simulations and conditional analyses, we observe variations in the intermittency depending on the intensity of the turbulence, the location in the flame, and the variable under consideration. We discuss the implications of these results for the flame structure and also provide an explanation for the observed results by considering the two-way interactions between turbulence and flames.
Bio
Dr. Peter Hamlington is an Assistant Professor in the Department of Mechanical Engineering at the University of Colorado, Boulder. His current research interests are in turbulence physics and modeling, combustion, and geophysical turbulent flows, with an emphasis on numerical and analytical approaches. Previously he was an Assistant Research Professor in the Department of Aerospace Engineering Sciences at the University of Colorado, Boulder and a National Research Council postdoctoral research associate in the Laboratories for Computational Physics and Fluid Dynamics at the Naval Research Laboratory (NRL) in Washington DC. He received both his M.S. and Ph.D. in Aerospace Science from the University of Michigan, and has a B.A. in Physics from the University of Chicago.