Counter-flow configurations, whereby two streams of fluid are brought together from opposite directions, are highly efficient mixers due to the high turbulence intensities that can be maintained.In this paper, a simplified version of the problem is introduced that is amenable to direct numerical simulation. The resulting turbulent flow problem is confined between two walls, with one non-zero mean velocity component varying in the space direction normal to the wall, corresponding to a simple shear flow. Compared to conventional channel flows, the mean flow is inflectional and the maximum turbulence intensity relative to the maximum mean velocity is nearly an order of magnitude higher. The numerical requirements and turbulence properties of this configuration are first determined. The Reynolds shear stress is required to vary linearly by the imposed forcing, with a peak at the channel centreline. A similar behaviour is observed for the streamwise Reynolds stress, the budget of which shows an approximately uniform distribution of dissipation, with large contributions from production, pressure-strain and turbulent diffusion. A viscous sublayer is obtained near the walls and with increasing Reynolds number small-scale streaks in the streamwise momentum are observed, superimposed on the large-scale structures that buffet this region. When the peak local mean Mach number reaches 0.55, turbulent Mach numbers of 0.6 are obtained, indicating that this flow configuration can be useful to study compressibility effects on turbulence.
I. INTRODUCTIONCounter-flow shear layers, also known as counter-current flows, have been previously recognised as efficient flow configurations for mixing [1-4], thrust vectoring (flow control)[5-7] and combustion [8,9]. Strykowski and Wilcoxon [2] showed that counter-current configurations could be used to control axisymmetric jet flows and enhance their mixing characteristics using global oscillations produced by self-excitation within shear layers. Strykowski and colleagues [8,9] also showed that a counter-current flow configuration can be used in swirl combustors to efficiently control the turbulent burning velocity (flame speed) and reduce pollutant emissions. The use of counter-flow configurations for fundamental flow studies was first recognised by Humphrey and Li [1] and later by various researchers including most notably Forliti et al. [3] who studied planar shear layers. A shear layer develops