scholarly journals Leaving flatland: Diagnostics for Lagrangian coherent structures in three-dimensional flows

2013 ◽  
Vol 258 ◽  
pp. 77-92 ◽  
Author(s):  
Mohamed H.M. Sulman ◽  
Helga S. Huntley ◽  
B.L. Lipphardt ◽  
A.D. Kirwan
Keyword(s):  
Coherent Structures ◽  
Three Dimensional ◽  
Lagrangian Coherent Structures

scholarly journals Lagrangian coherent structures in tropical cyclone intensification

2012 ◽  
Vol 12 (12) ◽  
pp. 5483-5507 ◽  
Author(s):  
B. Rutherford ◽  
G. Dangelmayr ◽  
M. T. Montgomery
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Flow Field ◽  
Coherent Structures ◽  
Finite Time ◽  
Potential Temperature ◽  
Three Dimensional ◽  
Lagrangian Coherent Structures ◽  
Moist Convection ◽  
Hyperbolic Structures

Abstract. Recent work has suggested that tropical cyclones intensify via a pathway of rotating deep moist convection in the presence of enhanced fluxes of moisture from the ocean. The rotating deep convective structures possessing enhanced cyclonic vorticity within their cores have been dubbed Vortical Hot Towers (VHTs). In general, the interaction between VHTs and the system-scale vortex, as well as the corresponding evolution of equivalent potential temperature (θe) that modulates the VHT activity, is a complex problem in moist helical turbulence. To better understand the structural aspects of the three-dimensional intensification process, a Lagrangian perspective is explored that focuses on the coherent structures seen in the flow field associated with VHTs and their vortical remnants, as well as the evolution and localized stirring of θe. Recently developed finite-time Lagrangian methods are limited in the three-dimensional turbulence and shear associated with the VHTs. In this paper, new Lagrangian techniques developed for three-dimensional velocity fields are summarized and we apply these techniques to study VHT and θe phenomenology in a high-resolution numerical tropical cyclone simulation. The usefulness of these methods is demonstrated by an analysis of particle trajectories. We find that VHTs create a locally turbulent mixing environment. However, associated with the VHTs are hyperbolic structures that span between adjacent VHTs or adjacent vortical remnants and represent coherent finite-time transport barriers in the flow field. Although the azimuthally-averaged inflow is responsible for the inward advection of boundary layer θe, attracting Lagrangian coherent structures are coincident with pools of high boundary layer θe. Extensions of boundary layer coherent structures grow above the boundary layer during episodes of convection and remain with the convective vortices. These hyperbolic structures form initially as boundaries between VHTs. As vorticity aggregates into a ring-like eyewall feature, the Lagrangian boundaries merge into a ring outside of the region of maximal vorticity.

Detection of Lagrangian coherent structures in three-dimensional turbulence

2007 ◽  
Vol 572 ◽  
pp. 111-120 ◽  
Author(s):  
M. A. GREEN ◽  
C. W. ROWLEY ◽  
G. HALLER
Keyword(s):  
Turbulent Flow ◽  
Coherent Structures ◽  
Computational Cost ◽  
Three Dimensional ◽  
Lagrangian Coherent Structures ◽  
Secondary Vortex ◽  
Hairpin Vortex ◽  
Coherent Vortices ◽  
Fully Developed Turbulent Flow ◽  
Eulerian Methods

We use direct Lyapunov exponents (DLE) to identify Lagrangian coherent structures in two different three-dimensional flows, including a single isolated hairpin vortex, and a fully developed turbulent flow. These results are compared with commonly used Eulerian criteria for coherent vortices. We find that despite additional computational cost, the DLE method has several advantages over Eulerian methods, including greater detail and the ability to define structure boundaries without relying on a preselected threshold. As a further advantage, the DLE method requires no velocity derivatives, which are often too noisy to be useful in the study of a turbulent flow. We study the evolution of a single hairpin vortex into a packet of similar structures, and show that the birth of a secondary vortex corresponds to a loss of hyperbolicity of the Lagrangian coherent structures.

scholarly journals Lagrangian Coherent Structures near a Subtropical Jet Stream

2010 ◽  
Vol 67 (7) ◽  
pp. 2307-2319 ◽  
Author(s):  
Wenbo Tang ◽  
Manikandan Mathur ◽  
George Haller ◽  
Douglas C. Hahn ◽  
Frank H. Ruggiero
Keyword(s):  
Coherent Structures ◽  
Three Dimensional ◽  
Wrf Model ◽  
Lagrangian Coherent Structures ◽  
Weather Research And Forecasting ◽  
Jet Stream ◽  
Forecast System ◽  
Subtropical Jet Stream ◽  
Subtropical Jet ◽  
Stability Results

Abstract Direct Lyapunov exponents and stability results are used to extract and distinguish Lagrangian coherent structures (LCS) from a three-dimensional atmospheric dataset generated from the Weather Research and Forecasting (WRF) model. The numerical model is centered at 19.78°N, 155.55°W, initialized from the Global Forecast System for the case of a subtropical jet stream near Hawaii on 12 December 2002. The LCS are identified that appear to create optical and mechanical turbulence, as evidenced by balloon data collected during a measurement campaign near Hawaii.

Investigation of Three-Dimensional Lagrangian Coherent Structures in Flow Past Single and Arrays of Plate: Linear Energy Harvesting Applications

2018 ◽  
Author(s):  
Bashar Attiya ◽  
I-Han Liu ◽  
Muhannad Altimemy ◽  
Cosan Daskiran ◽  
Alparslan Oztekin
Keyword(s):  
Coherent Structures ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Lagrangian Coherent Structures ◽  
Turbulent Structures ◽  
Single Plate ◽  
Flow Past ◽  
Finite Time Lyapunov Exponent ◽  
Large Eddy ◽  
Flow Interactions

Large Eddy Simulations (LES) are performed to investigate the coherent structures in flows past a single and an array of tandem plates. Lagrangian coherent structures (LCS) are used to investigate the nonlinear vortex dynamics of flow past a single plate. The Finite-Time Lyapunov Exponent (FTLE) is calculated using the velocity data obtained from Large Eddy Simulations (LES). All simulations are conducted at Reynolds number of 50,000. LCS for a single plate is presented in this study to elucidate and comprehend highly turbulent flow interactions in these flows. The LCS is compared against most commonly used Eulerian structures which are contours of the vorticity and the Q-criterion. The FTLE fields reveal much clearer turbulent structures compared to the Eulerian structures. FTLE better describes the evolution of larger scale eddies. The Q-criterion of flows past an array of plates is also presented.

scholarly journals Lagrangian coherent structures and entrainment near the turbulent/non-turbulent interface of a gravity current

2019 ◽  
Vol 877 ◽  
pp. 824-843 ◽  
Author(s):  
Marius M. Neamtu-Halic ◽  
Dominik Krug ◽  
George Haller ◽  
Markus Holzner
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Gravity Current ◽  
Three Dimensional ◽  
Lagrangian Coherent Structures ◽  
Flow Measurements ◽  
Vortical Structures ◽  
Entrainment Velocity ◽  
Extraction Algorithm ◽  
Entrainment Process

In this paper, we employ the theory of Lagrangian coherent structures for three-dimensional vortex eduction and investigate the effect of large-scale vortical structures on the turbulent/non-turbulent interface (TNTI) and entrainment of a gravity current. The gravity current is realized experimentally and different levels of stratification are examined. For flow measurements, we use a multivolume three-dimensional particle tracking velocimetry technique. To identify vortical Lagrangian coherent structures (VLCSs), a fully automated three-dimensional extraction algorithm for multiple flow structures based on the so-called Lagrangian-averaged vorticity deviation method is implemented. The size, the orientation and the shape of the VLCSs are analysed and the results show that these characteristics depend only weakly on the strength of the stratification. Through conditional analysis, we provide evidence that VLCSs modulate the average TNTI height, consequently affecting the entrainment process. Furthermore, VLCSs influence the local entrainment velocity and organize the flow field on both the turbulent and non-turbulent sides of the gravity current boundary.

scholarly journals Lagrangian coherent structures in tropical cyclone intensification

2011 ◽  
Vol 11 (10) ◽  
pp. 28125-28168 ◽  
Author(s):  
B. Rutherford ◽  
G. Dangelmayr ◽  
M. T. Montgomery
Keyword(s):  
Boundary Layer ◽  
Coherent Structures ◽  
Potential Temperature ◽  
Three Dimensional ◽  
Complex Problem ◽  
Lagrangian Coherent Structures ◽  
Moist Convection ◽  
Hyperbolic Structures ◽  
Convective Structures ◽  
Deep Moist Convection

Abstract. Recent work has suggested that tropical cyclones intensify via a pathway of rotating deep moist convection in the presence of enhanced fluxes of moisture from the ocean. The rotating deep convective structures possessing enhanced cyclonic vorticity within their cores have been dubbed Vortical Hot Towers (VHTs). In general, the interaction between VHTs and the system-scale vortex, as well as the corresponding evolution of equivalent potential temperature θe that modulates the VHT activity, is a complex problem in moist helical turbulence. To better understand the structural aspects of the three-dimensional intensification process, a Lagrangian perspective is explored that focuses on the localized stirring around VHTs and their vortical remnants, as well as the evolution and stirring of θe. Recently developed finite-time Lagrangian methods are limited in the three-dimensional turbulence and shear associated with the VHTs. In this paper, new Lagrangian techniques developed for three-dimensional velocity fields are summarized and we apply these techniques to study VHT and θe phenomenology. Our primary findings are that VHTs are coherent Lagrangian vortices that create a turbulent mixing environment. Associated with the VHTs are hyperbolic structures that modulate the aggregation of VHTs and their vortical remnants. Although the azimuthally-averaged inflow is responsible for the inward advection of boundary layer θe, the Lagrangian coherent structures are found to modulate the convection emanating from the boundary layer by stirring θe along organized attracting boundaries. Extensions of boundary layer coherent structures grow above the boundary layer during episodes of convection are responsible for organizing the remnants of the convective vortices. These hyperbolic structures form initially as boundaries between VHTs, but persist above the boundary layer and outlive the VHTs to eventually form the primary eyewall as the vortex attains maturity.

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