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Non-Linear Scale Interactions in a Forced Turbulent Boundary Layer

Citation

Duvvuri, Subrahmanyam (2016) Non-Linear Scale Interactions in a Forced Turbulent Boundary Layer. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9Z31WKP . http://resolver.caltech.edu/CaltechTHESIS:02292016-143116051

Abstract

This thesis explores the dynamics of scale interactions in a turbulent boundary layer through a forcing-response type experimental study. An emphasis is placed on the analysis of triadic wavenumber interactions since the governing Navier-Stokes equations for the flow necessitate a direct coupling between triadically consist scales. Two sets of experiments were performed in which deterministic disturbances were introduced into the flow using a spatially-impulsive dynamic wall perturbation. Hotwire anemometry was employed to measure the downstream turbulent velocity and study the flow response to the external forcing. In the first set of experiments, which were based on a recent investigation of dynamic forcing effects in a turbulent boundary layer, a 2D (spanwise constant) spatio-temporal normal mode was excited in the flow; the streamwise length and time scales of the synthetic mode roughly correspond to the very-large-scale-motions (VLSM) found naturally in canonical flows. Correlation studies between the large- and small-scale velocity signals reveal an alteration of the natural phase relations between scales by the synthetic mode. In particular, a strong phase-locking or organizing effect is seen on directly coupled small-scales through triadic interactions. Having characterized the bulk influence of a single energetic mode on the flow dynamics, a second set of experiments aimed at isolating specific triadic interactions was performed. Two distinct 2D large-scale normal modes were excited in the flow, and the response at the corresponding sum and difference wavenumbers was isolated from the turbulent signals. Results from this experiment serve as an unique demonstration of direct non-linear interactions in a fully turbulent wall-bounded flow, and allow for examination of phase relationships involving specific interacting scales. A direct connection is also made to the Navier-Stokes resolvent operator framework developed in recent literature. Results and analysis from the present work offer insights into the dynamical structure of wall turbulence, and have interesting implications for design of practical turbulence manipulation or control strategies.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:turbulent boundary layers; non-linear interactions.
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Awards:Kalam Prize for Aerospace Engineering, 2011. Charles D. Babcock Award, 2013. Donald Coles Prize in Aeronautics, 2016.
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • McKeon, Beverley J.
Group:Resnick Sustainability Institute
Thesis Committee:
  • Gharib, Morteza (chair)
  • Pullin, Dale Ian
  • Colonius, Timothy E.
  • McKeon, Beverley J.
Defense Date:8 January 2016
Funders:
Funding AgencyGrant Number
Air Force Office of Scientific ResearchFA 9550-12-1-0469
Record Number:CaltechTHESIS:02292016-143116051
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:02292016-143116051
DOI:10.7907/Z9Z31WKP
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9595
Collection:CaltechTHESIS
Deposited By: Subrahmanyam Duvvuri
Deposited On:04 Mar 2016 18:03
Last Modified:21 Feb 2017 18:02

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