Applied Physics Seminar, Finding order in chaos: Identifying and modeling coherent structures in turbulent flows

Turbulent flows are characterized by erratic velocity and thermodynamic fluctuations, but most turbulent flows also contain organized motions called coherent structures. These structures contribute significantly to quantities of interest such as drag, heat transfer, and noise emission, so the ability to identify, model, and manipulate coherent structures could lead to performance improvements in a wide range of engineering applications. This talk will focus on methods to identify and model coherent structures, using the canonical case of a turbulent jet as an illustrative example. I will show how coherent structures within the jet called wavepackets can be educed from data and modeled using concepts from linear stability theory and a new theoretical connection between a data-mining technique called spectral proper orthogonal decomposition and a modeling technique called resolvent analysis. Finally, the noise produced by the jet is reduced by manipulating the wavepackets using active control. Throughout the talk, I will emphasize the importance of using methods that account for the chaotic nature of turbulent flows via appropriate averaging, and I will conclude by highlighting opportunities to use these ideas to address important problems in physics and engineering.