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Low order modelling of flow-control techniques for turbulent skin-friction reduction
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Duque Daza, Carlos Alberto (2012) Low order modelling of flow-control techniques for turbulent skin-friction reduction. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2603114~S1
Abstract
In the present thesis a linearized formulation of the Navier-Stokes equations is used to study two main subjects:
the generation of near-wall streaks in turbulent boundary layers and the response of turbulent wall-bounded
flows to streamwise-travelling waves of spanwise oscillations of the bounding walls. For the purposes of the
present work, these oscillations of the wall have been considered as a flow control mechanism.
A mathematical model, based on a velocity-vorticity formulation linearized around a turbulent mean base flow,
is adopted to simulate the fluid flow equations. A hybrid spectral-finite differences solver has been employed
to numerically implement the linearized system.
A review on turbulent streak generation is presented and the concepts of exponential growth, algebraic growth
and viscous dissipation of small-scale perturbations are linked to the concept of transient growth. Mechanisms
of generation of near-wall streaks are explored using a large set of sources of excitation for the linearized Navier-
Stokes equations (LNSE). Two types of sources, here labelled as Excitation Mechanisms (EM), are employed:
a body-force source and an initial condition. The selection of parameters for the excitation mechanisms is
performed based on the definition of a multi-step optimization problem. The different EMs studied consist
of a restricted number of parameters, and therefore can be considered as a Low Order Model (LOM) for the
generation of streaks. It is shown that both types of EM produce satisfactory results for the streak generation
process evaluated in terms of experimentally expected optimal spanwise scales.
Finally, a large set of numerical experiments are conducted to evaluate the response of the LNSE with optimised
EM, to the flow control by a spanwise oscillating wall. By comparing the results between the response of the
LNSE considered here to this type of flow control against a drag-reduction map obtained by DNS in other
studies, it is possible to assess the correlation between streak evolution and disruption of the skin-friction drag.
A good agreement between these two responses is found for the parameter space of the streamwise-travelling
spanwise oscillation waves.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QA Mathematics T Technology > TA Engineering (General). Civil engineering (General) |
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Library of Congress Subject Headings (LCSH): | Skin friction (Aerodynamics), Navier-Stokes equations, Fluid dynamics -- Mathematical models, Turbulence | ||||
Official Date: | October 2012 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | School of Engineering | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Lockerby, Duncan A. | ||||
Extent: | xviii, 268 leaves : illustrations | ||||
Language: | eng |
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