# SIMPLE algorithm and its GAMG linear solver

Hi everyone,

I was looking at the help documents regarding the numerics of the simulation. I understand how the SIMPLE algorithm works regarding an iterative process that solves the momentum equations for the velocity field, then solves the poissons equation for pressure and then corrects the solved velocity field with the pressure so that it satisfies the continuity equation and then has to solve again as now the velocity field doesn’t satisfy the momentum equations.

But why is there a need for linear solvers like GAMG - in the help document ‘linear solvers used in computing each variable’ . Is the SIMPLE algorithm just setting up the method and then the solvers actually solve the linear equations in the matrix?

Additionally the numerical schemes are used to discretise the terms in the governing equations, how is this different to what GAMG is doing?

I think I have just got everything muddled in my head so any guidance and explanations would be greatly appreciated.

Thanks ( sorry if i have confused anyone)

Hi @hdog!

I would assume that this preconditioner is actually just use to make the numerical problem more easy to solve (would have to counter-check). Did you have a look at this page here: OpenFOAM: User Guide: GAMG Solver

P.S.: Maybe if there’s an expert in this topic from the CFD Squad, they can add their two cents here.

All the best!

Jousef