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Philipp Hack, CTR Postdoctoral Fellow, Stanford University

Event Type: 
Date and Time: 
Friday, January 27, 2017 - 16:30
CTR Conference Room 103
Event Sponsor: 
Parviz Moin, Director of Center for Turbulence Research

Visualizations of turbulent boundary layers show an abundance of characteristic arcshaped structures whose apparent similarity suggests a common origin in a coherent dynamic process. While the structures have been likened to the hairpin vortices observed in the late stages of transitional flow, a consistent description of the underlying mechanism has remained elusive. Detailed studies of coherent turbulent processes are complicated by the chaotic nature of the flow which modulates each manifestation and renders the isolation of representative samples a challenging task.

The present study harnesses methods developed in the field of computer vision to identify and analyze turbulent flow processes. The algorithm employs morphological operations to distill the topology of the turbulent flow field into a discrete graph. The low-dimensional structural information is stored in a database and enables the identification and analysis of equivalent dynamical processes across multiple scales. Application of the scheme to direct simulations data allows for the first time the time-resolved sampling of the turbulent hairpin process. The analysis attributes the hairpin process to an inviscid instability mechanism related to the inflection points introduced by turbulent streaks.

Dr. Philipp Hack received his Ph.D. from Imperial College London in 2014. His theoretical and computational work on the stability of boundary layers was awarded in 2013 with the EPSRC Doctoral Prize Fellowship and in 2015 with a DFG Research Fellowship. Philipp Hack joined the group of Professor Parviz Moin at the beginning of 2015. His current research interests include flow stability, optimization and machine learning.