Frequency selection by feedback control in a turbulent shear flow. (18th May 2016)

• Record Type: Journal Article
• Authors: Parezanović, Vladimir; Cordier, Laurent; Spohn, Andreas; Duriez, Thomas; Noack, Bernd R.; Bonnet, Jean-Paul; Segond, Marc; Abel, Markus; Brunton, Steven L.
• Is Part Of: Journal of fluid mechanics. Volume 797(2016:Jun.)
• Page Start: 247
• Page End: 283
• Publication Date: 2016-05-18
• Subjects: free shear layers, -- instability control, -- turbulence control; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2016.261
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : Many previous studies have shown that the turbulent mixing layer under periodic forcing tends to adopt a lock-on state, where the major portion of the fluctuations in the flow are synchronized at the forcing frequency. The goal of this experimental study is to apply closed-loop control in order to provoke the lock-on state, using information from the flow itself. We aim to determine the range of frequencies for which the closed-loop control can establish the lock-on, and what mechanisms are contributing to the selection of a feedback frequency. In order to expand the solution space for optimal closed-loop control laws, we use the genetic programming control (GPC) framework. The best closed-loop control laws obtained by GPC are analysed along with the associated physical mechanisms in the mixing layer flow. The resulting closed-loop control significantly outperforms open-loop forcing in terms of robustness to changes in the free-stream velocities. In addition, the selection of feedback frequencies is not locked to the most amplified local mode, but rather a range of frequencies around it.