  Turbulent transport of angular momentum is a necessary process to explain
accretion in astrophysical disks. Although the hydrodynamic stability of
disk-like flows has been tested in experiments, results are contradictory and
suggest either laminar or turbulent flow. Direct numerical simulations reported
here show that currently investigated laboratory flows are hydrodynamically
unstable and become turbulent at low Reynolds numbers. The underlying
instabilities stem from the axial boundary conditions, affect the flow globally
and enhance angular-momentum transport.
