Laminar-Turbulent Transition

Using spectral and space-time modal decompositions to discover amplification mechanisms and symmetry breaking during laminar-turbulent transition in wall-bounded shear flows. Applied to K- and H-type transition scenarios to extract nonlinear flow structures and estimate energy transfer functions.

Selected Publications

2024

Modal Decomposition of K- and H-Type Boundary Layer Transition

C. Lin, and O. T. Schmidt

AIAA Paper 2024-0495, 2024

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We perform a data-driven discovery of the physics within transition mechanisms by using a suite of modal decomposition techniques on the DNS of deterministic K-type boundary layer transition. Specifically, we deploy Spectral Proper Orthogonal Decomposition (SPOD) and Space-Time POD (STPOD) along with a D1 Symmetry Decomposition to educe coherent structures in time and frequency domain, with different optimality properties each, and establish their relationships to each other. Our study is in part a data-driven counterpart to a recent harmonic balancing study by Rigas et al. [1]: Therein we verify which pre-turbulence transition mechanisms are reproducible by a varying number of Fourier-type modes at the fundamental frequency and its harmonics. In extension, we identify from data the prototypical transition scenario, extract modes associated with various instability mechanisms and uncover how far these distinct coherent structures persevere into the developed turbulence. We investigate energetic exchanges in the transitional and turbulent regimes with particular emphasis on the emergence of periodic and non-periodic, as well as symmetric and anti-symmetric structures within the flow.