Comparison of two definitions of Lagrangian coherent structures in fluid flows and their numerical implementations
Date Issued
2010
Date
2010
Author(s)
Wen, Cheng-Yu
Abstract
The mixing of passive tracers in two-dimensional fluid flows is intimately linked to the presence of coherent structures. Without being specific about their definition for now, we shall picture these structures, and refer to them as Lagrangian coherent structures.
We introduce two definitions of Lagrangian coherent structures in two-dimensional turbulence. The first definition is Hyperbolic Time Approach(HTA), the second is Finite-Time Lyapunov Exponents(FTLE). The Lagrangian coherent structures are defined as material lines that are stable or unstable for longer times than any of their neighbors. Such material lines are responsible for stretching and folding in the mixing of passive tracers. Therefore, we can find these structures to know mixing effect is stronger than nearby trajectorys.
Finally, we compare two approaches and illustrate the results on 2-D unsteady flows.
Subjects
Coherent structures
Mixing
Finite-time Lyapunov exponents
Hyperbolic time approach
Type
thesis
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