An Algebraic Multigrid Solver for the Navier-Stokes Problems
                 in the Discrete Second-Order Approximation.

                                  R Webster
            Roadside, Harpsdale, Halkirk, Caithness, KW12 6Ul. UK.

                                  G Robinson
        Northeast Parallel Architectures Centre, Syracuse University,
                           Syracuse, NY 13244, USA.


An algebraic multigrid scheme is presented for solving the discrete
Navier-Stokes equations to second-order accuracy using the defect-correction
method.  Solutions for the driven cavity and for the asymmetric, sudden
expansion test problems have been obtained for both structured and
unstructured meshes, the resolution and resolution grading being controlled by
global and local mesh refinements.

The solver is efficient and robust to the extent that no under-relaxation of
variables is required to ensure convergence but rates of convergence can be
improved with small amounts of under-relaxation of the velocity-pressure
coupling.  Providing the computational mesh can resolve the flow field,
convergence characteristics are almost mesh independent.  Rates of convergence
actually improve with refinement, asymptotically approaching mesh independent
values.  For extremely coarse meshes where dispersive truncation errors would
be expected to prevent convergence (or even induce divergence), solutions can
still be obtained by using explicit under-relaxation in the iterative cycle.


KEYWORDS: Algebraic Multigrid, Defect Correction, Unstructured Meshes.