Segregated solvers employ a solution strategy where the momentum equations are first solved, using a guessed pressure, and an equation for a pressure correction is obtained. Because of the ‘guess-and-correct’ nature of the linear system, a large number of iterations are typically required in addition to the need for judiciously selecting relaxation parameters for the variables.

Ansys CFX uses a coupled solver, which solves the hydrodynamic equations (for u, v, w, p) as a single system. This solution approach uses a fully implicit discretization of the equations at any given time step. For steady-state problems, the time-step behaves like an ‘acceleration parameter’, to guide the approximate solutions in a physically based manner to a steady-state solution. This reduces the number of iterations required for convergence to a steady-state, or to calculate the solution for each time step in a time-dependent analysis.