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Transition delay in boundary layer flow using feedback control
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.ORCID iD: 0000-0002-8209-1449
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-4346-4732
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.ORCID iD: 0000-0001-7864-3071
(English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645Article in journal (Other academic) Submitted
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-29750OAI: oai:DiVA.org:kth-29750DiVA: diva2:397412
Note
QC 20110214Available from: 2011-02-14 Created: 2011-02-14 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Feedback control and modal structures in transitional shear flows
Open this publication in new window or tab >>Feedback control and modal structures in transitional shear flows
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

 

Two types of shear flows are investigated in this thesis; numerical simulations are performed for the analysis and control of the perturbation arising in a boundary layer over a flat plate, whereas PIV measurements are analysed for the investigation of a confined turbulent jet. Modal structures of the flows are identified: the aim is to understand the flow phenomena and to identify reduced-order models for the feedback control design. The attenuation of three-dimensional wavepackets of streaks and Tollmien-Schlichting (TS) waves in the boundary layer is obtained using feedback control based on arrays of spatially localized sensors and actuators distributed near the rigid wall. In order to tackle the difficulties arising due to the dimension of the discretized Navier-Stokes operator, a reduced-order model is identified, preserving the dynamics between the inputs and the outputs; to this end, approximate balanced truncation is used. Thus, control theory tools can be easily handled using the low-order model. We demonstrate that the energy growth of both TS wavepackets and streak-packets is substantially and efficiently mitigated, using relatively few sensors and actuators. The robustness of the controller is investigated by varying the number of actuators and ensors, the Reynolds number and the pressure gradient. The configuration can be possibly reproduced in experiments, due to the localization of sensing and actuation devices. A complete analysis of a confined turbulent jet is carried out using timeresolved PIV measurements. Proper orthogonal decomposition (POD) modes and Koopman modes are computed and analysed for understanding the main features of the flow. The frequencies related to the dominating mechanisms are identified; the most energetic structures show temporal periodicity.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. vii, 33 p.
Series
Trita-MEK, ISSN 0348-467X ; 2011:01
Keyword
flow control, flat-plate boundary layer, laminar-turbulent transition
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-29754 (URN)978-91-7415-863-2 (ISBN)
Presentation
2011-02-18, Sal E3, KTH, Osquars backe 14, Stockhkolm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish e‐Science Research Center
Note
QC 20110214Available from: 2011-02-14 Created: 2011-02-14 Last updated: 2012-05-24Bibliographically approved

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Bagheri, ShervinBrandt, LucaHenningson, Dan S.

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