  Incompressible fluids on curved surfaces are considered with respect to the
interplay between topology, geometry and fluid properties using a surface
vorticity-stream function formulation, which is solved using parametric finite
elements. Motivated by designed examples for superfluids, we consider the
influence of a geometric potential on vortices for fluids with finite viscosity
and show numerical examples in which a change in the geometry is used to
manipulate the flow field.
