  We study the effect of different boundary conditions on the kinematic dynamo
threshold of von Karman type swirling flows in a cylindrical geometry. Using an
analytical test flow, we model different boundary conditions: insulating walls
all over the flow, effect of sodium at rest on the cylinder side boundary,
effect of sodium behind the impellers, effect of impellers or side wall made of
a high-magnetic-permeability material. We find that using
high-magnetic-permeability boundary conditions decreases the dynamo threshold,
the minimum being achieved when they are implemented all over the flow.
