J. Fluid Mech. (2014), vol. 745, pp. 300–320. c  Cambridge University Press 2014 doi:10.1017/jfm.2014.99 300 Spanwise reflection symmetry breaking and turbulence control: plane Couette flow G. Chagelishvili 1, 2, 4 , G. Khujadze 1, 3, †, H. Foysi 3 and M. Oberlack 4, 5 1 Abastumani Astrophysical Observatory, Ilia State University, Tbilisi 0160, Georgia 2 M. Nodia Institute of Geophysics, Tbilisi State University, Tbilisi 0128, Georgia 3 Chair of Fluid Mechanics, Universität Siegen, Paul-Bonatz-Str. 9-11, 57068 Siegen, Germany 4 Chair of Fluid Dynamics, Technische Universität Darmstadt, Darmstadt 64287, Germany 5 GS Comp. Engineering, Technische Universität Darmstadt, Darmstadt 64287, Germany (Received 10 May 2013; revised 11 December 2013; accepted 18 February 2014) We propose and analyse a new strategy of shear flow turbulence control that can be realized by the following steps: (i) imposing specially designed seed velocity perturbations, which are non-symmetric in the spanwise direction, at the walls of a flow; (ii) the configuration of the latter ensures a gain of shear flow energy and the breaking of turbulence spanwise reflection symmetry: this leads to the generation of spanwise mean flow; (iii) that changes the self-sustained dynamics of turbulence and results in a considerable reduction of the turbulence level and the production of turbulent kinetic energy. In fact, by this strategy the shear flow transient growth mechanism is activated and the formed spanwise mean flow is an intrinsic, nonlinear composition of the controlled turbulence and not directly introduced in the system. In the present paper, a weak near-wall volume forcing is designed to impose the velocity perturbations with required characteristics in the flow. The efficiency of the proposed scheme has been demonstrated by direct numerical simulation using plane Couette flow as a representative example. A promising result was obtained: after a careful parameter selection, the forcing reduces the turbulence kinetic energy and its production by up to one-third. The strategy can be naturally applied to other wall-bounded flows, e.g. channel and boundary-layer flows. Of course, the considered volume force is theoretical and hypothetical. Nevertheless, it helps to gain knowledge concerning the design of the seed velocity field that is necessary to be imposed in the flow to achieve a significant reduction of the turbulent kinetic energy. This is convincing with regard to a new control strategy, which could be based on specially constructed blowing/suction or riblets, by employing the insight gained by the comprehension of the results obtained using the investigated methodology in this paper. Key words: flow control, turbulence control, turbulent flows † Email address for correspondence: george.khujadze@uni-siegen.de