  Large-scale instabilities occurring in the presence of small-scale turbulent
fluctuations are frequently observed in geophysical or astrophysical contexts
but are difficult to reproduce in the laboratory. Using extensive numerical
simulations, we report here on intense recurrent bursts of turbulence in plane
Poiseuille flow rotating about a spanwise axis. A simple model based on the
linear instability of the mean flow can predict the structure and time scale of
the nearly-periodic and self-sustained burst cycles. Rotating Poiseuille flow
is suggested as a prototype for future studies of low-dimensional dynamics
embedded in strongly turbulent environments.
