报告题目: |
The Transition to Turbulence in Shear Flows: The Edge of Chaos and Multiple Edge States |
报告人: |
Lina Kim |
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报告时间: |
2009-12-21 16:00 |
报告地点: |
物理系三楼报告厅 |
主办单位: |
物理系 |
简介: |
内容提要：
The transition to turbulence in linearly stable shear flows is one of
the most intriguing and outstanding problems in classical physics.
Turbulent dynamics are readily observed at flow speeds where the
laminar state remains stable under infinitesimal perturbations.
Moreover, for a smaller class of shear flows, such as plane Couette
and pipe flows, linear stability theory predicts that the laminar
state remains stable for all Reynolds numbers. However, numerical
simulations and experiments provide evidence that these flows exhibit
turbulence, which can decay spontaneously, for sufficiently high
Reynolds numbers and perturbations. These observations are in
agreement with a chaotic saddle coexisting with the laminar state in
the system's state space. Analyzing the 'Edge of Chaos' between
laminar and turbulent dynamics for these systems have generated
additional insight into the transition mechanism. This boundary
contains edge states which are too weak to become turbulent and too
strong to laminarize can be either dynamically simple or complex
structures. To identify the edge states, we employ an iterated edge
tracking algorithm which is implemented for several refinements until
we find a trajectory which neither becomes turbulent or laminarizes.
We show that for edge states with a stable manifold of codimension 1
(i.e., only unstable direction), the edge tracking algorithm will
converge to it. We study the edge states for various channel sizes
and compare their dynamics to those of edge states for other shear
flows.
报告人简介：
Lina Kim received a BS in Mechanical Engineering from the University
of California Riverside in 1999, an MS and PhD in Mechanical
Engineering from the University of California Santa Barbara,
respectively in 2005 and 2009. Her current research interests focus
on investigating the transition to turbulence via edge state
mechanisms in shear flows such as sinusoidal shear flow, plane Couette
flow, pipe flow, and plane Poiseuille flow. Current topics of
interest include the role of linear transient energy growth in the
transition to turbulence, turbulence control, applying edge of chaos
ideas to large-scale interconnected and biological systems. She is
currently a junior specialist and postdoctoral researcher with Jeff
Moehlis at the University of California Santa Barbara. |
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