  This paper describes a new multilevel procedure that can solve the discrete
Navier-Stokes system arising from finite volume discretizations on composite
grids, which may consist of more than one level. SIMPLE is used and tested as
the smoother, but the multilevel procedure is such that it does not exclude the
use of other smoothers. Local refinement is guided by a criterion based on an
estimate of the truncation error. The numerical experiments presented test not
only the behaviour of the multilevel algebraic solver, but also the efficiency
of local refinement based on this particular criterion.
