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

Marius M. Neamtu-Halic*, Dominik Krug, George Haller, Markus Holzner

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

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.

Original languageEnglish
Pages (from-to)824-843
Number of pages20
JournalJournal of fluid mechanics
Volume877
DOIs
Publication statusPublished - 25 Oct 2019

Fingerprint

entrainment
Gravitation
gravitation
Flow measurement
Flow structure
stratification
Vorticity
Velocity measurement
Flow fields
Vortex flow
flow measurement
vorticity
flow distribution
vortices
deviation

Keywords

  • UT-Hybrid-D
  • stratified turbulence
  • turbulent mixing
  • gravity currents

Cite this

@article{ebbdf929c97a4e54bcf9b7812a6e6524,
title = "Lagrangian coherent structures and entrainment near the turbulent/non-Turbulent interface of a gravity current",
abstract = "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.",
keywords = "UT-Hybrid-D, stratified turbulence, turbulent mixing, gravity currents",
author = "Neamtu-Halic, {Marius M.} and Dominik Krug and George Haller and Markus Holzner",
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year = "2019",
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language = "English",
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Lagrangian coherent structures and entrainment near the turbulent/non-Turbulent interface of a gravity current. / Neamtu-Halic, Marius M.; Krug, Dominik; Haller, George; Holzner, Markus.

In: Journal of fluid mechanics, Vol. 877, 25.10.2019, p. 824-843.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Lagrangian coherent structures and entrainment near the turbulent/non-Turbulent interface of a gravity current

AU - Neamtu-Halic, Marius M.

AU - Krug, Dominik

AU - Haller, George

AU - Holzner, Markus

N1 - Cambridge University Press deal

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Y1 - 2019/10/25

N2 - 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.

AB - 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.

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