TURBULENT PLANE COUETTE-FLOW SUBJECT TO STRONG SYSTEM ROTATION

System rotation is known to substantially affect the mean flow pattern as well as the turbulence structure in rotating channel flows. In a n umerical study of plane Couette flow rotating slowly about an axis ali gned with the mean vorticity, Bech & Andersson (1996a) found that the turbulence level was damped in the presence of anticyclonic system rot ation, in spite of the occurrence of longitudinal counter-rotating rol l cells. Moreover, the turbulence anisotropy was practically unaffecte d by the weak rotation, for which the rotation number Ro, defined as t he ratio of twice the imposed angular vorticity Omega to the shear rat e of the corresponding laminar flow, was +/-0.01. The aim of the prese nt paper is to explore the effects of stronger anticyclonic system rot ation on directly simulated turbulent plane Couette flow. Turbulence s tatistics like energy, enstrophy and Taylor lengthscales, both compone ntal and directional, were computed from the statistically steady flow fields and supplemented by structural information obtained by conditi onal sampling. The designation of the imposed system rotation as 'high ' was associated with a reversal of the conventional Reynolds stress a nisotropy so that the velocity fluctuations perpendicular to the wall exceeded those in the streamwise direction. It was observed that the a nisotropy reversal was accompanied by an appreciable region of the mea n velocity profile with slope similar to 2 Omega, i.e. the absolute me an vorticity tended to zero. It is particularly noteworthy that these characteristic features were shared by two fundamentally different flo w regimes. First, the two-dimensional roll cell pattern already observ ed at Ro = 0.01 became more regular and energetic at Ro = 0.10 and 0.2 0, whereas the turbulence level was reduced by about 50%. Then, when R o was further increased to 0.50, a disordering of the predominant roll cell pattern set in during a transient period until the flow field se ttled at a new statistically steady state substantially less affected by the roll cells. This was accompanied by a substantial amplification of the streamwise turbulent vorticity and an anomalous variation of t he mean turbulent kinetic energy which peaked in the middle of the cha nnel rather than near the walls. While the predominant flow structures of the non-rotating flow were longitudinal streaks, system rotation g enerated streamwise vortices, either ordered secondary flow or quasi-s treamwise vortices. Eventually, at Ro = 1.0, the turbulent fluctuation s were completely suppressed and the flow field relaminarized.