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  • 1.
    Morra, Pierluigi
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Sasaki, K.
    Cavalieri, A.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.
    Control of streaky disturbances in the boundary layer over a flat plate2018In: 31st Congress of the International Council of the Aeronautical Sciences, ICAS 2018, International Council of the Aeronautical Sciences , 2018Conference paper (Refereed)
    Abstract [en]

    The present work considers control of perturbations in the boundary layer over a flat plate by means of adaptive methods. In particular, we focus our attention on a control law based on a multi-input-multi-output (MIMO) filtered-x least-mean-square (fxLMS) adaptive algorithm. The studies are performed through direct numerical simulations. The perturbation field studied here mimics those generated by freestream turbulence with different amplitude and scales. Plasma actuators and shear-stress sensors are considered to mimic a real case scenario.

  • 2.
    Morra, Pierluigi
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Semeraro, Onofrio
    Univ Paris Saclay, LIMSI, UPR 3251 CNRS, F-91400 Orsay, France..
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Cossu, Carlo
    Cent Nantes, LHEEA, UMR 6598, CNRS, F-44300 Nantes, France..
    On the relevance of Reynolds stresses in resolvent analyses of turbulent wall-bounded flows2019In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 867, p. 969-984, article id PII S0022112019001964Article in journal (Refereed)
    Abstract [en]

    The ability of linear stochastic response analysis to estimate coherent motions is investigated in turbulent channel flow at the friction Reynolds number Re-r = 1007. The analysis is performed for spatial scales characteristic of buffer-layer and large-scale motions by separating the contributions of different temporal frequencies. Good agreement between the measured spatio-temporal power spectral densities and those estimated by means of the resolvent is found when the effect of turbulent Reynolds stresses, modelled with an eddy-viscosity associate with the turbulent mean flow, is included in the resolvent operator. The agreement is further improved when the flat forcing power spectrum (white noise) is replaced with a power spectrum matching the measures. Such a good agreement is not observed when the eddy-viscosity terms are not included in the resolvent operator. In this case, the estimation based on the resolvent is unable to select the right peak frequency and wall-normal location of buffer-layer motions. Similar results are found when comparing truncated expansions of measured streamwise velocity power spectral densities based on a spectral proper orthogonal decomposition to those obtained with optimal resolvent modes.

  • 3. Sasaki, K.
    et al.
    Morra, Pierluigi
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Cavalieri, A. V. G.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.
    On the wave-cancelling nature of boundary layer transition control2018In: 31st Congress of the International Council of the Aeronautical Sciences, ICAS 2018, International Council of the Aeronautical Sciences , 2018Conference paper (Refereed)
    Abstract [en]

    This work deals with the feedforward active control of velocity fluctuations over incompressible 3D boundary layers. Two strategies are evaluated, the Linear Quadratic Gaussian (LQG) controller, built using the eigensystem realization algorithm (ERA), is compared to a wave-cancellation scheme, obtained via the direct inversion of the frequency-domain transfer functions of the system. For the evaluated cases, it is shown that LQG leads to a wave-cancelling signal of the incoming Tollmien-Schlichting wavepacket. Such result allows further insight into the physics behind the active control of convectively unstable flows permitting, for instance, the optimization of the transverse position for actuation via a linear stability approach.

  • 4.
    Sasaki, Kenzo
    et al.
    ITA, Aerodynam Dept, Sao Jose Dos Campos, Brazil..
    Morra, Pierluigi
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fabbiane, Nicolo
    French Aerosp Lab ONERA, Dept Fundamental & Expt Aerodynam, Palaiseau, France..
    Cavalieri, Andre V. G.
    ITA, Aerodynam Dept, Sao Jose Dos Campos, Brazil..
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    On the wave-cancelling nature of boundary layer flow control2018In: Theoretical and Computational Fluid Dynamics, ISSN 0935-4964, E-ISSN 1432-2250, Vol. 32, no 5, p. 593-616Article in journal (Refereed)
    Abstract [en]

    This work deals with the feedforward active control of Tollmien-Schlichting instability waves over incompressible 2D and 3D boundary layers. Through an extensive numerical study, two strategies are evaluated; the optimal linear-quadratic-Gaussian (LQG) controller, designed using the Eigensystem realization algorithm, is compared to a wave-cancellation scheme, which is obtained using the direct inversion of frequency-domain transfer functions of the system. For the evaluated cases, it is shown that LQG leads to a similar control law and presents a comparable performance to the simpler, wave-cancellation scheme, indicating that the former acts via a destructive interference of the incoming wavepacket downstream of actuation. The results allow further insight into the physics behind flow control of convectively unstable flows permitting, for instance, the optimization of the transverse position for actuation. Using concepts of linear stability theory and the derived transfer function, a more efficient actuation for flow control is chosen, leading to similar attenuation of Tollmien-Schlichting waves with only about 10% of the actuation power in the baseline case.

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