Lagrangian coherent structure identification using a Voronoi tessellation-based networking algorithm

Rosi, Giuseppe; Walker, Andrew; Rival, David E.

doi:10.1007/s00348-015-2061-0

Cited by 14 publications

(11 citation statements)

References 17 publications

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“…FTLE and FSLE methods have seen wide usage in both experimental [37,38,39,40] and observational [42,43,47,83,84,85,46,49,50,51] contexts.…”

Section: Lcs Diagnostic Methodsmentioning

confidence: 99%

“…We specify an unsteady velocity field v that has seen extensive use as a testbed for LCS analysis [142,143,109,144,1,145,38,146,102,77,147,78,79,148,76,88]: the double gyre flow as introduced by Shadden et al [75]. The velocity v = (v 1 , v 2 ) takes the form where the function h is defined by…”

Section: Passive Scalar Advectionmentioning

confidence: 99%

“…The key point is whatever the definitions of LCSs, their formulation is typically (with a few exceptions, such as, for example, the burning manifolds of [32,33,34,35,36]) based solely on the Lagrangian trajectories associated with (1), and the goal is to identify fluid parcel groups that behave similarly, and are thus 'coherent.' This has been a rich area of study using both experimental [37,38,39,40] and observational [41,42,43,44,45,46,47,48,49,50,51,52,53] data.…”

Section: Introductionmentioning

confidence: 99%

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Generalized Lagrangian coherent structures

Balasuriya

Ouellette

Rypina

2018

Physica D: Nonlinear Phenomena

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The notion of a Lagrangian Coherent Structure (LCS) is by now well established as a way to capture transient coherent transport dynamics in unsteady and aperiodic fluid flows that are known over finite time. We show that the concept of an LCS can be generalized to capture coherence in other quantities of interest that are transported by, but not fully locked to, the fluid. Such quantities include those with dynamic, biological, chemical, or thermodynamic relevance, such as temperature, pollutant concentration, vorticity, kinetic energy, plankton density, and so on. We provide a conceptual framework for identifying the Generalized Lagrangian Coherent Structures (GLCSs) associated with such evolving quantities. We show how LCSs can be seen as a special case within this framework, and provide an overarching discussion of various methods for identifying LCSs. The utility of this more general viewpoint is highlighted through a variety of examples. We also show that although LCSs approximate GLCSs in certain limiting situations under restrictive assumptions on how the velocity field affects the additional quantities of interest, LCSs are not in general sufficient to describe their coherent transport.

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“…FTLE and FSLE methods have seen wide usage in both experimental [37,38,39,40] and observational [42,43,47,83,84,85,46,49,50,51] contexts.…”

Section: Lcs Diagnostic Methodsmentioning

confidence: 99%

Section: Passive Scalar Advectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Generalized Lagrangian coherent structures

Balasuriya

Ouellette

Rypina

2018

Physica D: Nonlinear Phenomena

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“…This can be mitigated by using various Eulerian measures to identify coherent vortices, such as the ∆, λ, and Q criteria which are derived from a decomposition of the local velocity gradient tensor. [36][37][38] While these Eulerian measures can be extremely useful, they suffer some drawbacks: 37,38 they typically require a user-defined threshold and therefore the identified boundaries of vortices are subjective, and they do not contain any information on the history of the flow. An alternative approach that overcomes these issues is to identify the wake mode and the Lagrangian structures from the FTLE fields computed in forward-and backward-time, which correspond to the repelling and attracting structures in the flow, respectively.…”

Section: Introductionmentioning

confidence: 99%

“…An alternative approach that overcomes these issues is to identify the wake mode and the Lagrangian structures from the FTLE fields computed in forward-and backward-time, which correspond to the repelling and attracting structures in the flow, respectively. This approach is often used to approximate the LCSs and is capable of revealing the complex processes governing flows, 12,39,40 identifying regions of strong or weak mixing, 38,41 as well as producing strikingly beautiful visualisations. 42 This paper aims to provide new insight into the dynamics and Lagrangian structures associated with the various wake modes observed in streamwise VIV and to investigate their effect on fluid mixing.…”

Section: Introductionmentioning

confidence: 99%

Lagrangian structures and mixing in the wake of a streamwise oscillating cylinder

Cagney

Balabani

2016

Physics of Fluids

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Lagrangian analysis is capable of revealing the underlying structure and complex phenomena in unsteady flows. We present particle-image velocimetry measurements of the wake of a cylinder undergoing streamwise vortex-induced vibrations and calculate the Finite-Time Lyapunov Exponents (FTLE) in backward- and forward-time. The FTLE fields are compared to the phase-averaged vorticity fields for the four different wake modes observed while the cylinder experiences streamwise vortex-induced vibrations. The backward-time FTLE fields characterise the formation of vortices, with the roll up of spiral-shaped ridges coinciding with the roll up of the shear layers to form the vortices. Ridges in the forward-time fields tend to lie perpendicular to the flow direction and separate nearby vortices. The shedding of vortices coincides with a “peel off” process in the forward-time FTLE fields, in which a ridge connected to the cylinder splits into two strips, one of which moves downstream. Particular attention is given to the “wake breathing” process, in which the streamwise motion of the cylinder causes both shear layers to roll up simultaneously and two vortices of opposite sign to be shed into the wake. In this case, the ridges in forward-time FTLE fields are shown to define “vortex cells,” in which the new vortices form, and the FTLE fields allow the wake to be decomposed into three distinct regions. Finally, the mixing associated with each wake mode is examined, and it is shown that cross-wake mixing is significantly enhanced when the vibration amplitude is large and the vortices are shed alternately. However, while the symmetric shedding induces large amplitude vibrations, no increase in mixing is observed relative to the von Kármán vortex street observed behind near-stationary bodies.

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