Change search
ReferencesLink to record
Permanent link

Direct link
Feedback Control for Laminarization of flow over Wings
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-5913-5431
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0001-7864-3071
2015 (English)In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 94, no 1, 43-62 p.Article in journal (Refereed) Published
Abstract [en]

An active control strategy is implemented to attenuate the amplitude of the Tollmien-Schlichting (TS) waves inside the boundary layer of an airfoil. The dynamics of the system are modelled by the linearised Navier-Stokes equations. The impulse response to an initial disturbance, initially located outside of the boundary layer and in front of the airfoil is considered. The perturbation evolves and penetrates inside the boundary layer and triggers the TS waves. Different control strategies including the linear quadratic Gaussian (LQG) and model predictive control (MPC) are designed based on a reduced order model where the sensors and actuators are localised near the wall. An output projection is used to identify the unstable disturbances; the objective function of the controller is selected as a set of proper orthogonal decomposition (POD) modes; to isolate the dynamics of the TS waves, the modes with high energy contents in the TS wave frequency band are considered as the objective of the controller. A plasma actuator is modelled and implemented as an external forcing on the flow. To account for the limitations of the plasma actuator several strategies are examined and the results are compared with a classical LQG controller. The outcomes reveal successful performance in mitigating the amplitude of the wavepacket developing inside the boundary layer.

Place, publisher, year, edition, pages
2015. Vol. 94, no 1, 43-62 p.
Keyword [en]
Active Flow Control, Boundary Layer, Tollmien-Schlichting wavepacket
National Category
Mechanical Engineering
URN: urn:nbn:se:kth:diva-145659DOI: 10.1007/s10494-014-9578-9ISI: 000347407100003OAI: diva2:719481

QC 20150209. Updated from manuscript to article in journal.

Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2015-02-09Bibliographically approved
In thesis
1. Flow control and reduced-order modelling of transition in shear flows
Open this publication in new window or tab >>Flow control and reduced-order modelling of transition in shear flows
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis direct numerical simulation is used to investigate the possibility to delay the transition from a laminar to a turbulent flow in boundary layer flows. Furthermore, modal analysis techniques are used to identify the coherent structures in wind turbine wake.

Among different transition scenarios, the classical transition scenario is considered where the laminar-turbulent transition occursdue to Tollmien-Schlichting (TS) waves. These waves are convectively unstable and when triggered inside the boundary layer, they grow exponentially inamplitude as they are advected downstream of the domain. The aim is to suppressthese waves using flow control strategies based on a row of spatially localised sensors and actuators distributed near the wall inside the boundary layer. To avoid the high dimensionality arising from discretisation of the Navier–Stokes equations, a reduced order model (ROM) based on the Eigensystem Realisation Algorithm(ERA) is obtained and based on that a linear controller is designed. To manip-ulate the flow, a plasma actuator is modelled and implementedas an externalforcing. To account for the restrictions of the plasma actuators, several strategies are proposed and tested within the LQG framework. We studied also the design of a faster controller based on decentralised approach and compared the performance to a more expensive centralised controller. The outcomes revea lsuccessful performance in mitigating the energy of the disturbances inside the boundary layer and suppressing the TS waves.

To extract coherent features of the wind turbine wakes, modal decomposition techniques are employed. In this method a large dynamical system is reduced to a fewer number of degrees of freedom. Two decomposition techniques are employed, namely proper orthogonal decomposition and dynamic mode decomposition. In the former, the flow is decomposed into a set of orthogonal structures which are ranked according to their energy contents in a hierarchical manner. In the latter, the eigenvalues and eigenvectors of the underlying approximate linear operator of the system is evaluated. In particular each mode is associated with a specific frequency and growth rate. The results revealed the coherent structures which are dynamically significant for the onset of instability in the wind turbine wake

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. vii, 57 p.
TRITA-MEK, ISSN 0348-467X ; 2014:14
Flow control, plasma actuator, wing, leading edge, flat plate, wind turbine, optimal controller, model reduction, proper orthogonal decomposition, dynamic mode decomposition.
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-145631 (URN)978-91-7595-170-6 (ISBN)
Public defence
2014-06-10, Sal F3, Lindstedtsvägen 26. KTH, Stockholm, 10:15 (English)

QC 20140526

Available from: 2014-05-26 Created: 2014-05-23 Last updated: 2014-05-26Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Search in DiVA

By author/editor
Dadfar, RezaHanifi, ArdeshirHenningson, Dans S.
By organisation
Stability, Transition and ControlLinné Flow Center, FLOWMechanics
In the same journal
Flow Turbulence and Combustion
Mechanical Engineering

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 144 hits
ReferencesLink to record
Permanent link

Direct link