  The turbulent transport of angular momentum plays an important role in many
astrophysical objects, but its modelization is still far from satisfactory. We
discuss here what can be learned from laboratory experiments. We analyze the
results obtained by Wendt (1933) and Taylor (1936) on the classical
Couette-Taylor flow, in the case where angular momentum increases with distance
from the rotation axis, which is the most interesting for astrophysical
applications. We show that when the gap between the coaxial cylinders is wide
enough, the criterion for the onset of the finite amplitude instability can be
expressed in terms of a gradient Reynolds number. Based on Wendt's results, we
argue that turbulence may be sustained by differential rotation when the
angular velocity decreases outward, as in keplerian flows. From the rotation
profiles and the torque measurements we deduce a prescription for the turbulent
viscosity which is independent of gap width; with some caution it may be
applied to stellar interiors and to accretion disks.
