MAE 298 Seminar: OWNS, NOWNS, and Unknowns: Efficient and robust tools for transition prediction

Abstract: Accurately predicting instability and transition to turbulence in boundary layers is critical for aerodynamic design but remains challenging for complex geometries and hypersonic flows. A longstanding difficulty is computational: global stability methods capable of capturing strongly nonparallel effects can be prohibitively expensive. Beyond this familiar challenge lies a more fundamental one - the disturbances that trigger transition are often poorly characterized or unknown, motivating the use of optimization and uncertainty-quantification tools to infer, bound, and identify the relevant disturbance environment. In this talk, I will discuss the One-Way Navier-Stokes (OWNS) equations, a streamwise-marching framework that retains important nonparallel physics while achieving computational costs comparable to parabolized approaches such as PSE. I will then describe extensions aimed at addressing these additional unknowns: nonlinear OWNS (NOWNS) captures interactions among growing instability waves and the early stages of transition; inverse formulations identify upstream disturbances from downstream observations; and a new receptivity framework uses optimization to determine which combinations of acoustic, vortical, and entropic free-stream disturbances most effectively excite boundary-layer instabilities. Together, these methods provide a computationally efficient framework for connecting uncertain disturbance environments to receptivity, amplification, and nonlinear transition in realistic high-speed aerodynamic configurations.

Bio: Tim Colonius is the Frank and Ora Lee Marble Professor of Mechanical Engineering and Medical Engineering at the California Institute of Technology. He is also the Executive Officer for Mechanical and Civil Engineering and holds the Cecil and Sally Drinkward Leadership Chair. He received his B.S. from the University of Michigan in 1987 and M.S and Ph.D. in Mechanical Engineering from Stanford University in 1988 and 1994, respectively. He and his research team use numerical simulations and data-driven analysis to study a range of problems in fluid dynamics, including aeroacoustics, reduced-order modeling, flow control, instabilities, shock waves, and multiphase flow. He also investigates medical applications of ultrasound and cavitation. Prof. Colonius is a Fellow of the American Physical Society and the Acoustical Society of America. He was the recipient of the 2018 AIAA Aeroacoustics Award, the 2021 APS-DFD Stanley Corrsin Award, and he was the 2022 ASME Freeman Scholar. He is an author of more than 350 publications, and he is the former editor-in-chief of the journal Theoretical and Computational Fluid Dynamics.