  We numerically solve the magnetic induction equation in a spherical shell
geometry, with a kinematically prescribed axisymmetric flow that consists of a
superposition of a small-scale helical flow and a large-scale shear flow. The
small-scale flow is chosen to be a local analog of the classical Roberts cells,
consisting of strongly helical vortex rolls. The large-scale flow is a shearing
motion in either the radial or the latitudinal directions. In the absence of
large-scale shear, the small-scale flow is an efficient dynamo, in agreement
with previous results. Adding increasingly large shear flows strongly
suppresses the dynamo efficiency, indicating that shear is not always a
favourable ingredient in dynamo action.
