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Nonlinear optimal control of transition due to a pair of vortical perturbations using a receding horizon approach

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Title: Nonlinear optimal control of transition due to a pair of vortical perturbations using a receding horizon approach
Authors: Xiao, D
Papadakis, G
Item Type: Journal Article
Abstract: This paper considers the nonlinear optimal control of transition in a boundary layer flow subjected to a pair of free stream vortical perturbations using a receding horizon approach. The optimal control problem is solved using the Lagrange variational technique that results in a set of linearized adjoint equations, which are used to obtain the optimal wall actuation (blowing and suction from a control slot located in the transition region). The receding horizon approach enables the application of control action over a longer time period, and this allows the extraction of time-averaged statistics as well as investigation of the control effect downstream of the control slot. The results show that the controlled flow energy is initially reduced in the streamwise direction and then increased because transition still occurs. The distribution of the optimal control velocity responds to the flow activity above and upstream of the control slot. The control effect propagates downstream of the slot and the flow energy is reduced up to the exit of the computational domain. The mean drag reduction is and in the control region and downstream of the slot, respectively. The control mechanism is investigated by examining the second-order statistics and the two-point correlations. It is found that in the upstream (left) side of the slot, the controller counteracts the near-wall high-speed streaks and reduces the turbulent shear stress; this is akin to opposition control in channel flow, and because the time-average control velocity is positive, it is more similar to blowing-only opposition control. In the downstream (right) side of the slot, the controller reacts to the impingement of turbulent spots that have been produced upstream and inside the boundary layer (top–bottom mechanism). The control velocity is positive and increases in the streamwise direction, and the flow behaviour is similar to that of uniform blowing.
Issue Date: 25-Feb-2019
Date of Acceptance: 5-Nov-2018
URI: http://hdl.handle.net/10044/1/66232
DOI: https://dx.doi.org/10.1017/jfm.2018.919
ISSN: 0022-1120
Publisher: Cambridge University Press (CUP)
Start Page: 524
End Page: 555
Journal / Book Title: Journal of Fluid Mechanics
Volume: 861
Copyright Statement: © 2018 Cambridge University Press. This paper has been accepted for publication and will appear in a revised form, subsequent to peer-review and/or editorial input by Cambridge University Press.
Keywords: Science & Technology
Technology
Physical Sciences
Mechanics
Physics, Fluids & Plasmas
Physics
boundary layer control
transition to turbulence
DIRECT NUMERICAL-SIMULATION
TURBULENT-BOUNDARY-LAYERS
FRICTION DRAG REDUCTION
SKIN-FRICTION
SPANWISE SLOT
SUBJECT
DNS
01 Mathematical Sciences
09 Engineering
Fluids & Plasmas
Publication Status: Published
Online Publication Date: 2018-12-27
Appears in Collections:Aeronautics
Faculty of Engineering