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On the origin of drag increase in varying-phase opposition control

Toedtli, Simon and Yu, Christine and McKeon, Beverley (2020) On the origin of drag increase in varying-phase opposition control. International Journal of Heat and Fluid Flow, 85 . Art. No. 108651. ISSN 0142-727X.

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This study investigates the physics underlying the drag increase in a low Reynolds number turbulent channel flow due to varying-phase opposition control by means of direct numerical simulation and modal analysis. The drag increase occurs for an extended region of the parameter space and we consider a controller with a positive phase shift in Fourier domain between sensor measurement and actuator response as a representative example for this regime. Analyses of instantaneous flow fields as well as spatial power spectra show that the structure of drag-increased flows is remarkably different from that of drag-reduced and canonical flows. In particular, the near-wall region is dominated by structures of short streamwise and large spanwise extent. Isolation of a representative control scale shows that these energetic structures can be characterized as spanwise rollers, which induce strong ejection and sweep motions and lead to drag increase. The presence of rollers, and therefore drag increase, in the full nonlinear system correlates well with the presence of an amplified eigenvalue in the eigenspectrum of the linearized Navier–Stokes operator. It is further shown that the scales responsible for drag increase at positive phase shifts are inactive at negative phase shifts and do not contribute to drag reduction. These scales can therefore be excluded from a controller aimed at drag reduction, which relaxes the spatial resolution requirements on the control hardware. The eigenspectrum may be used as a computationally cheap tool to identify such detrimental scales during an early design stage.

Item Type:Article
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McKeon, Beverley0000-0003-4220-1583
Additional Information:© 2020 Elsevier Inc. Received 1 April 2020, Revised 4 June 2020, Accepted 24 June 2020, Available online 4 August 2020.
Subject Keywords:Wall-bounded turbulence; Turbulent flow control
Record Number:CaltechAUTHORS:20200805-102610802
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Official Citation:Simon Toedtli, Christine Yu, Beverley McKeon, On the origin of drag increase in varying-phase opposition control, International Journal of Heat and Fluid Flow, Volume 85, 2020, 108651, ISSN 0142-727X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104755
Deposited By: Tony Diaz
Deposited On:05 Aug 2020 18:53
Last Modified:05 Aug 2020 18:53

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