Solver Settings

How the flow solver iterates: pressure-velocity coupling and under-relaxation, the choice of compressible solver, the convection schemes, the non-orthogonal correction and the start of the run. Every setting has an auto value that follows the rest of the case. The step is shown only when fluid flow is selected.

Last updated 2026-11-03

What this step does

Coupling and relaxation. The steady solvers use SIMPLE (Patankar and Spalding, 1972); the "SIMPLEC" switch selects its consistent variant (Van Doormaal and Raithby, 1984) (OpenFOAM consistent yes), which needs no pressure relaxation. On auto, the relaxation factors Pressure relaxation, Velocity relaxation, Turbulent kinetic energy relaxation, Specific dissipation rate relaxation and, for compressible runs, Density relaxation and Energy relaxation follow the switch. The compressible solver uses plain SIMPLE on auto whatever the switch says. The presets "Reset to auto" and "Conservative" (p 0.3, U 0.7, k and ω 0.3, ρ 0.1, SIMPLEC off) fill the fields.

Compressible solver. For steady compressible runs, Compressible solver selects steady SIMPLE, transonic SIMPLE or the pseudo-transient solver; the last has its own Local Courant number (pseudo-transient).

Schemes. Momentum (U) convection scheme (U, and energy for compressible runs) and k and ω convection scheme ( $k$ and $\omega$ after the start-up phase). Laplacian and surface-normal gradients use Gauss linear limited corrected with the limiter of Non-orthogonal correctors.

Start of the run. Initialise with the potential-flow solver computes a potential-flow initial field; Upwind iterations before the switch sets the length of the first-order start-up phase, after which the solver restarts with the final schemes and relaxation.

Divergence fallback. The start-up phase counts as diverged on NaN or very large residuals, a solver that stops without an error message, a time step that collapses, or a pressure held at its limits in every one of the last 50 iterations. The run then restarts once from the initial fields with plain SIMPLE (p 0.3, U 0.7, k 0.7, ω 0.7, ρ 0.1), or, for the pseudo-transient solver, at half the Courant number. A second failure stops the run with the reason.

Source

The auto rules for relaxation, the non-orthogonal correctors, the compressible solver and the convection schemes, and the measurements behind each default, are given in the field articles. OpenFOAM dictionaries: (OpenFOAM user guide, 2026).

Valid range

Auto first

Change a setting from auto only for a specific reason (a diverging start, a stalled residual); each field article states the measurements behind its default.

Fields in this step 13

Field	Symbol	Unit	Default
Compressible solver Experimental			auto: steady SIMPLE up to inlet Mach 0.2, pseudo-transient above
Density relaxation	$\alpha_\rho$		auto: 0.1 (compressible SIMPLE), 1.0 (SIMPLEC with a typed p, transonic SIMPLE)
Energy relaxation	$\alpha_e$		auto: 0.7; 0.9 with SIMPLEC and heat transfer; 0.8 (transonic SIMPLE)
Initialise with the potential-flow solver			on
k and ω convection scheme			auto: limitedLinear 1
Local Courant number (pseudo-transient) Experimental	$Co_{max}$		0.5 (start-up phase: the smaller of this and 0.2)
Momentum (U) convection scheme			auto: linearUpwind (limited gradient)
Non-orthogonal correctors	$N_{no}$		auto: 1 (mesh below 60°), 2 (60-70°, or no mesh yet), 3 (above 70°)
Pressure relaxation	$\alpha_p$		auto: 1.0 (SIMPLEC), 0.3 (plain SIMPLE and every compressible run except transonic), 1.0 (transonic SIMPLE)
Specific dissipation rate relaxation	$\alpha_\omega$		auto: 0.7 (SIMPLEC and plain SIMPLE), 0.9 (transonic SIMPLE)
Turbulent kinetic energy relaxation	$\alpha_k$		auto: 0.7 (SIMPLEC and plain SIMPLE), 0.9 (transonic SIMPLE)
Upwind iterations before the switch	$N_{up}$	iterations	200
Velocity relaxation	$\alpha_U$		auto: 0.7 in the start-up phase, 0.9 after it (SIMPLEC); 0.7 (plain SIMPLE, compressible); 0.9 (transonic SIMPLE)

What this step does

Source

Valid range

Fields in this step 13

Related 13

References 3