FLUENT solver contains two forms of multigrid: algebraic (AMG) and
full-approximation storage (FAS). AMG is an essential component of both the pressure-based and density-based implicit solvers, while FAS is an important, but optional, component of the density-based explicit solver. (Note that when the density-based explicit solver is used, AMG will also be used, since the scalar equations (e.g., turbulence) are solved using the approach described in Section 25.2.)
This section describes the mathematical basis of the multigrid approach. Common aspects of AMG and FAS are presented first, followed by separate sections that provide details unique to each method. Information about user inputs and controls for the multigrid solver is provided in Sections 25.22.3 and 25.11.2.