
If you are performing a steadystate calculation, the governing equations for the pressurebased solver do not contain timedependent terms. For steadystate flows,
Section
25.3 describes controlvolumebased discretization of the steadystate transport equation (see Equation
25.21).
UnderRelaxation of Variables
The underrelaxation of variables is used in all cases for some material properties, in the NITA solver for solution variables, and in the pressurebased coupled algorithm where this explicit underrelaxation is used for momentum and pressure.
Because of the nonlinearity of the equation set being solved by FLUENT, it is necessary to control the change of . This is typically achieved by underrelaxation of variables (also referred to as explicit relaxation), which reduces the change of produced during each iteration. In a simple form, the new value of the variable within a cell depends upon the old value, , the computed change in , , and the underrelaxation factor, , as follows:
UnderRelaxation of Equations
The underrelaxation of equations, also known as implicit relaxation, is used in the pressurebased solver to stabilize the convergence behavior of the outer nonlinear iterations by introducing selective amounts of in the system of discretized equations. This is equivalent to the locationspecific time step.
The CFL number is a solution parameter in the pressurebased coupled algorithm and can be written in terms of :