Zero-absolute-vorticity state in a rotating turbulent shear flow

Stability characteristics of a rotating simple shear flow modulated periodically in the shear direction is investigated by direct numerical simulation. The temporal evolution and the final profile of the mean flow are examined, starting with a random perturbation imposed on it under the assumption that the velocity and pressure fields are uniform in the mean flow direction. It is found that the mean velocity profile changes due to the shear-Coriolis instability. If there is a locally unstable region in a stable rotating simple shear, the mean velocity profile there is deformed into a linear one with nearly-zero absolute vorticity. An analogy holds between rotating uniformly sheared turbulence and thermally convective turbulence that the region of nearly-zero absolute vorticity in the former corresponds to that of nearly-uniform temperature in the latter. (C) 2000 American Institute of Physics.