Seminar: Input/Output Analysis of High-speed Flows

Abstract

Input/output (I/O) analysis is applied to study the linearized dynamics of high speed jets and hypersonic boundary layers. Both of these flows support instability waves that amplify small perturbations. In high speed jets, instability wavepackets have been shown to be responsible for noise generation processes, determining the frequency and directivity of far-field acoustic radiation. Nichols' group has shown that I/O analysis recovers these wavepackets in good agreement with data from high-fidelity simulations and experiments. While such wavepackets may be computed from traditional methods of linear stability analysis, I/O analysis reveals additional, sub-optimal modes of noise production that recover information about sideline noise generation that the standard methods miss. The group furthermore demonstrates the utility of I/O analysis for understanding hypersonic boundary layer instabilities leading to laminar-to-turbulent transition.  Like the jet noise problem, the group shows that I/O analysis not only recovers the results of traditional methods  for canonical configurations, but provides additional insights about the linearized dynamics of the flow.  Also, unlike traditional stability methods, I/O analysis may be extended to complex geometries. The group has applied it to explain the nosetip bluntness paradox involving transition reversal in hypersonic flows past blunt cones. This research is supported by ONR grant N00014-17-1-2496, and by a grant of computer resources at the Argonne Leadership Computing Facility through the INCITE program.

About the speaker

Joe Nichols received his PhD from University of Washington in 2005. He subsequently worked at Stanford University as a post-doctoral fellow and research associate until 2013, after which he joined the University of Minnesota. He has been a pioneer in combining mathematics with simulation to generate advanced understanding of fluid flows. Nichols will discuss his recent efforts on developing and using the input/output analysis to resolve puzzling observations that have defied understanding for decades.

Hosted by Prof. Datta Gaitonde.