Linear instability and resonance effects in large-scale opposition flow control. (25th March 2022)

• Record Type: Journal Article
• Authors: Guseva, Anna; Jiménez, Javier
• Is Part Of: Journal of fluid mechanics. Volume 935(2022)
• Publication Date: 2022-03-25
• Subjects: turbulence control -- channel flow; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2022.34
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract: Abstract : Opposition flow control is a robust strategy that has been proved effective in turbulent wall-bounded flows. Its conventional set-up consists of measuring wall-normal velocity in the buffer layer and opposing it at the wall. This work explores the possibility of implementing this strategy with a detection plane in the logarithmic layer, where control could be feasible experimentally. We apply control on a channel flow at $Re_\tau = 932$, only on the eddies with relatively large wavelengths ( $\lambda / h > 0.1$ ). Similarly to the buffer layer opposition control, our control strategy results in a virtual-wall effect for the wall-normal velocity, creating a minimum in its intensity. However, it also induces a large response in the streamwise velocity and Reynolds stresses near the wall, with a substantial drag increase. When the phase of the control lags with respect to the detection plane, spanwise-homogeneous rollers are observed near the channel wall. We show that they are a result of a linear instability. In contrast, when the control leads with respect to the detection plane, this instability is inactive and oblique waves are observed. Their wall-normal profiles can be predicted linearly as a response of the turbulent channel flow to a forcing with the advection velocity of the detection plane. The linearity, governing the flow, opens a possibility to affect large scales of the flow in a controlled manner, when enhanced turbulence intensity or mixing is desired.