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Lagrangian and vortex-surface fields in turbulence

Citation

Yang, Yue (2011) Lagrangian and vortex-surface fields in turbulence. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:02212011-233246689

Abstract

In this thesis, we focus on Lagrangian investigations of isotropic turbulence, wall-bounded turbulence and vortex dynamics. In particular, the evolutionary multi-scale geometry of Lagrangian structures is quantified and analyzed. Additionally, we also study the dynamics of vortex-surface fields for some simple viscous flows with both Taylor--Green and Kida--Pelz initial conditions. First, we study the non-local geometry of finite-sized Lagrangian structures in both stationary, evolving homogenous isotropic turbulence and also with a frozen turbulent velocity field. The multi-scale geometric analysis is applied on the evolution of Lagrangian fields, obtained by a particle-backward-tracking method, to extract Lagrangian structures at different length scales and to characterize their non-local geometry in a space of reduced geometrical parameters. Next, we report a geometric study of both evolving Lagrangian, and also instantaneous Eulerian structures in turbulent channel flow at low and moderate Reynolds numbers. A multi-scale and multi-directional analysis, based on the mirror-extended curvelet transform, is developed to quantify flow structure geometry including the averaged inclination and sweep angles of both classes of turbulent structures at multiple scales ranging from the half-height of the channel to several viscous length scales. Results for turbulent channel flow include the geometry of candidate quasi-streamwise vortices in the near-wall region, the structural evolution of near-wall vortices, and evidence for the existence and geometry of structure packets based on statistical inter-scale correlations. In order to explore the connection and corresponding representations between Lagrangian kinematics and vortex dynamics, we develop a theoretical formulation and numerical methods for computation of the evolution of a vortex-surface field. Iso-surfaces of the vortex-surface field define vortex surfaces. A systematic methodology is developed for constructing smooth vortex-surface fields for initial Taylor--Green and Kida--Pelz velocity fields by using an optimization approach. Equations describing the evolution of vortex-surface fields are then obtained for both inviscid and viscous incompressible flows. Numerical results on the evolution of vortex-surface fields clarify the continuous vortex dynamics in viscous Taylor--Green and Kida--Pelz flows including the vortex reconnection, rolling-up of vortex tubes, vorticity intensification between anti-parallel vortex tubes, and vortex stretching and twisting. This suggests a possible scenario for explaining the transition from a smooth laminar flow to turbulent flow in terms of topology and geometry of vortex surfaces.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:turbulence theory, vortex dynamics, topological fluid mechanics, turbulent boundary layers, turbulent structures, multi-scale analysis
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Pullin, Dale Ian
Thesis Committee:
  • Pullin, Dale Ian (chair)
  • Leonard, Anthony
  • Hou, Thomas Y.
  • Meiron, Daniel I.
Defense Date:18 February 2011
Funders:
Funding AgencyGrant Number
NSFDMS-0714050
NSFDMS-1016111
Record Number:CaltechTHESIS:02212011-233246689
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:02212011-233246689
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6251
Collection:CaltechTHESIS
Deposited By: Yue Yang
Deposited On:29 Mar 2011 16:31
Last Modified:01 Aug 2014 17:12

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