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A robust control approach to understanding nonlinear mechanisms in shear flow turbulence

Citation

Maynard Gayme, Dennice (2010) A robust control approach to understanding nonlinear mechanisms in shear flow turbulence. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:05272010-195149679

Abstract

A robust control framework is used to investigate a streamwise constant projection of the Navier Stokes equations for plane Couette flow. Study of this streamwise constant model is motivated by both numerical and experimental observations that suggest the prevalence and importance of streamwise and quasi-streamwise elongated structures. Small-amplitude Gaussian noise forcing is applied to a two-dimensional, three-velocity component (2D/3C) model to describe its response in the presence of disturbances, uncertainty and modeling errors. A comparison of the results with Direct Numerical Simulation (DNS) data demonstrates that the simulations capture salient features of fully developed turbulence. In particular, the change in mean velocity profile from the nominal laminar to the characteristic “S” shaped turbulent profile. The application of Taylor’s hypothesis shows that the model can also reproduce downstream information in the form of large-scale coherence resembling numerically and experimentally observed flow features. The 2D/3C model is able to generate “turbulent-like” behavior under small-amplitude stochastic noise. The laminar flow solution is globally stable, therefore transition to turbulence in this model is likely a consequence of the laminar flow solution’s lack of robustness in the presence of disturbances and uncertainty. In fact, large disturbance amplification is common in both this model and the linearized Navier Stokes equations. Periodic spanwise/wall-normal (z–y) plane stream functions are used as input to develop a forced 2D/3C streamwise velocity equation. The resulting steady-state solution is qualitatively similar to a fully turbulent spatial field of DNS data. Both numerical methods and a perturbation analysis confirm that the momentum transfer that produces a “turbulent-like” mean profile requires a nonlinear streamwise velocity equation. A system theoretic approach is used to study the amplification mechanisms that develop through the 2D/3C nonlinear coupling in the streamwise velocity equation. The spanwise/wall-normal plane forcing required to produce each stream function is computedand used to define an induced norm from this forcing input to the streamwise velocity. This input-output response is used to determine the energy optimal spanwise wavelength (i.e.,the preferential spacing) over a range of Reynolds numbers and forcing amplitudes.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Shear flow turbulence; Coherent structures in Couette flow; Energy amplification; Nonlinear mechanisms in shear flow turbulence; Streamwise constant flow; Transition to turbulence as a robustness problem
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Control and Dynamical Systems
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Doyle, John Comstock
Thesis Committee:
  • Marsden, Jerrold E.
  • McKeon, Beverley J.
  • Bamieh, Bassam
  • Doyle, John Comstock (chair)
Defense Date:19 May 2010
Author Email:dennice (AT) cds.caltech.edu
Record Number:CaltechTHESIS:05272010-195149679
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05272010-195149679
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:5871
Collection:CaltechTHESIS
Deposited By: Dennice Maynard Gayme
Deposited On:04 Jun 2010 16:41
Last Modified:26 Dec 2012 03:26

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