Centralised Versus Decentralised Active Control of Boundary Layer Instabilities

Dadfar, Reza; Fabbiane, Nicolò; Bagheri, Shervin; Henningson, Dans S.

doi:10.1007/s10494-014-9552-6

Cited by 6 publications

(2 citation statements)

References 23 publications

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“…The main drawback of a fully centralizedcontrol approach is that the number of connections for a flat plate of large span quickly becomes impractical due to all the wiring. One may then introduce a semi-decentralized controller [95], where small MIMO control-units are designed and connected to each other; in [95], it is shown that a number of control-units can efficiently replace a full centralized control with a limited lost of performance.…”

Section: Discussionmentioning

confidence: 99%

Adaptive and Model-Based Control Theory Applied to Convectively Unstable Flows

Fabbiane

Semeraro

Bagheri

et al. 2014

Applied Mechanics Reviews

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Adaptive and model-based control theory applied to convectively unstable flows. Review, 66(6) Research on active control for the delay of laminar-turbulent transition in boundary layers has made a significant progress in the last two decades, but the employed strategies have been many and dispersed. Using one framework, we review model-based techniques, such as linear-quadratic regulators, and model-free adaptive methods, such as least-mean square filters. The former are supported by a elegant and powerful theoretical basis, whereas the latter may provide a more practical approach in the presence of complex disturbance environments, that are difficult to model. We compare the methods with a particular focus on efficiency, practicability and robustness to uncertainties. Each step is exemplified on the one-dimensional linearized Kuramoto-Sivashinsky equation, that shows many similarities with the initial linear stages of the transition process of the flow over a flat plate. Also, the source code for the examples are provided. Applied Mechanics

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Section: Discussionmentioning

confidence: 99%

Adaptive and Model-Based Control Theory Applied to Convectively Unstable Flows

Fabbiane

Semeraro

Bagheri

et al. 2014

Applied Mechanics Reviews

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“…Contrary to the feedback structure, the feedforward design is unconditionally stable, and its implementation via LQG synthesis is not a problem. Therefore, feedforward configurations combined with LQG syntheses dominate the noise-amplifier flow control literature, particularly in the incompressible boundary layer control studies (Bagheri et al 2009;Semeraro et al 2011Semeraro et al , 2013aDadfar et al 2013Dadfar et al , 2014Sasaki et al 2018aSasaki et al , 2020Freire et al 2020;Morra et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Reactive control of second Mack mode in a supersonic boundary layer with free-stream velocity/density variations

et al. 2023

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We consider closed-loop control of a two-dimensional supersonic boundary layer at $M=4.5$ that aims at reducing the linear growth of second Mack mode instabilities. These instabilities are first characterized with local spatial and global resolvent analyses, which allow us to refine the control strategy and to select appropriate actuators and sensors. After linear input–output reduced-order models have been identified, multi-criteria structured mixed $H_{2}$ / $H_{\infty }$ synthesis allows us to fix beforehand the controller structure and to minimize appropriate norms of various transfer functions: the $H_{2}$ norm to guarantee performance (reduction of perturbation amplification in nominal condition), and the $H_{\infty }$ norm to maintain performance robustness (with respect to sensor noise) and stability robustness (with respect to uncertain free-stream velocity/density variations). Both feedforward and feedback set-ups, i.e. with estimation sensor placed respectively upstream/downstream of the actuator, allow us to maintain the local perturbation energy below a given threshold over a significant distance downstream of the actuator, even in the case of noisy estimation sensors or free-stream density variations. However, the feedforward set-up becomes completely ineffective when convective time delays are altered by free-stream velocity variations of $\pm$ 5 %, which highlights the strong relevance of the feedback set-up for performance robustness in convectively unstable flows.

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Energy efficiency and performance limitations of linear adaptive control for transition delay

2016

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A reactive control technique with localised actuators and sensors is used to delay the transition to turbulence in a flat-plate boundary-layer flow. Through extensive direct numerical simulations, it is shown that an adaptive technique, which computes the control law on-line, is able to significantly reduce skin-friction drag in the presence of random three-dimensional perturbation fields with linear and weakly nonlinear behaviour. An energy budget analysis is performed in order to assess the net energy saving capabilities of the linear control approach. When considering a model of the dielectric-barrier-discharge (DBD) plasma actuator, the energy spent to create appropriate actuation force inside the boundary layer is of the same order as the energy gained from reducing skin-friction drag. With a model of an ideal actuator a net energy gain of three orders of magnitude can be achieved by efficiently damping small-amplitude disturbances upstream. The energy analysis in this study thus provides an upper limit for what we can expect in terms of drag-reduction efficiency for linear control of transition as a means for drag reduction.

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Centralised Versus Decentralised Active Control of Boundary Layer Instabilities

Cited by 6 publications

References 23 publications

Adaptive and Model-Based Control Theory Applied to Convectively Unstable Flows

Adaptive and Model-Based Control Theory Applied to Convectively Unstable Flows

Reactive control of second Mack mode in a supersonic boundary layer with free-stream velocity/density variations

Energy efficiency and performance limitations of linear adaptive control for transition delay

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