Journal ArticleDOI
Control of turbulent boundary layers
TLDR
In this article, the authors highlight the importance of a certain linear mechanism and its contribution to skin-friction drag in turbulent boundary layers and the implication that significant drag reduction can be achieved by altering this linear mechanism.Abstract:
The objective of this paper is to give an overview of recent progress on boundary layer control made by the author’s research group at University of California, Los Angeles. A primary theme is to highlight the importance of a certain linear mechanism and its contribution to skin-friction drag in turbulent boundary layers—and the implication that significant drag reduction can be achieved by altering this linear mechanism. Examples that first led to this realization are presented, followed by applications of linear optimal control theory to boundary-layer control. Results from these applications, in which the linear mechanism in turbulent channel flow was targeted, indirectly confirm the importance of linear mechanisms in turbulent—and hence, nonlinear—flows. Although this new approach has thus far been based solely on numerical experiments which are yet to be verified in the laboratory, they show great promise and represent a fundamentally new approach for flow control. The success and limitations of various controllers and their implications are also discussed.read more
Citations
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Journal ArticleDOI
Contribution of Reynolds stress distribution to the skin friction in wall-bounded flows
TL;DR: In this article, a simple expression is derived of the componential contributions that different dynamical effects make to the frictional drag in turbulent channel, pipe and plane boundary layer flows, which is used for an analysis of the drag modification by the opposition control and by the uniform wall blowing/suction.
Journal ArticleDOI
Closed-Loop Turbulence Control: Progress and Challenges
Steven L. Brunton,Bernd R. Noack +1 more
Journal ArticleDOI
Componentwise energy amplification in channel flows
TL;DR: In this article, the authors studied the linearized Navier-stokes (LNS) equations in channel flows from an input-output point of view by analysing their spatio-temporal frequency responses.
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A Linear Systems Approach to Flow Control
John Kim,Thomas Bewley +1 more
TL;DR: The objective of this paper is to introduce the essential ingredients of linear systems and control theory to the fluid mechanics community, to discuss the relevance of this theory to important open problems in the optimization, control, and forecasting of practical flow systems of engineering interest.
Journal ArticleDOI
Dynamics and Control of Global Instabilities in Open-Flows: A Linearized Approach
TL;DR: In this article, the dynamics and control of low-frequency unsteadiness, as observed in some aerodynamic applications, were addressed, and a coherent and rigorous linearized approach was presented, which enables both to describe the dynamics of commonly encountered open-flows and to design open-loop and closed-loop control strategies, in view of suppressing or delaying instabilities.
References
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Book
Robust and Optimal Control
TL;DR: This paper reviewed the history of the relationship between robust control and optimal control and H-infinity theory and concluded that robust control has become thoroughly mainstream, and robust control methods permeate robust control theory.
Journal ArticleDOI
Turbulence statistics in fully developed channel flow at low reynolds number
TL;DR: In this article, a direct numerical simulation of a turbulent channel flow is performed, where the unsteady Navier-Stokes equations are solved numerically at a Reynolds number of 3300, based on the mean centerline velocity and channel half-width, with about 4 million grid points.
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The structure of turbulent boundary layers
TL;DR: In this article, the authors describe the formation of low-speed streaks in the region very near the wall, which interact with the outer portions of the flow through a process of gradual lift-up, then sudden oscillation, bursting, and ejection.
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DIRECT NUMERICAL SIMULATION: A Tool in Turbulence Research
Parviz Moin,Krishnan Mahesh +1 more
TL;DR: In this article, direct numerical simulation (DNS) of turbulent flows has been reviewed and the complementary nature of experiments and computations in turbulence research has been illustrated, as well as how DNS has impacted turbulence modeling and provided further insight into the structure of turbulent boundary layers.