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Theses

Reduced-order models for linear dynamics and control in aerodynamics

Abstract : In aerodynamics, separated flows are often subject to strong instabilities which result in the shedding of large-scale vortices. Such low-frequency unsteadiness are commonly encountered in aeronautical applications and lead to detrimental effects such as severe structural vibrations or the generation of extensive noise pollution. This thesis aims at providing low-order models of such aerodynamic flows in order to design optimal control devices. The transitional backward-facing step flow is considered as a prototype of unstable separated flow. Firstly, the linear flow dynamics are examined using a global stability analysis. The flow is found to selectively amplify the upstream noise through the Kelvin-Helmholtz instability. Next, we use projection methods to construct low-order models of the linear two-dimensional dynamics of the flow. Three approaches are investigated: (i) the use of the least damped global modes, (ii) the Proper Orthogonal Decomposition (POD) and (iii) the balanced truncation. This thesis introduces a snapshot method in the frequency domain to compute the leading controllable, observable and balanced modes, as well as techniques to handle large fluid systems. Lastly, the question of the closed-loop control of the flow is addressed. An effective reduction of the perturbations is obtained by using a Linear Quadratic Gaussian compensator designed from a POD model.
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Contributor : Grégory Dergham <>
Submitted on : Monday, July 11, 2011 - 5:45:23 PM
Last modification on : Friday, July 17, 2020 - 2:56:29 PM
Long-term archiving on: : Monday, November 12, 2012 - 10:50:10 AM

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  • HAL Id : pastel-00607946, version 1

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Grégory Dergham. Reduced-order models for linear dynamics and control in aerodynamics. Mechanics of the fluids [physics.class-ph]. Arts et Métiers ParisTech, 2011. English. ⟨NNT : 2011ENAM0023⟩. ⟨pastel-00607946⟩

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