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Parameter · 06 Solver Settings

Initialise with the potential-flow solver

numerics.initialize_with_potential_foam Step 06 · Solver Settings

Before the solver starts, the program computes an inviscid, irrotational (potential) flow that satisfies continuity and the inlet and outlet conditions, and uses its velocity as the initial field.

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Theory

Without this option the solver starts from zero velocity in the whole domain. The potential-flow solver solves a Laplace equation for a velocity potential Φ\Phi whose source is the divergence of the initial flux, equation (1), and corrects the flux with its gradient so that it is divergence free, equation (2) (OpenFOAM user guide, 2026).

  • The boundary fluxes come from the inlet conditions. For a mass-flow or volume-flow inlet the program writes the uniform velocity −nQ/A-\mathbf{n}Q/A into the inlet's value entry, because the potential-flow solver builds its inlet flux from that entry; a zero entry would leave the potential solve without effect.
  • The equation is solved with 10 non-orthogonal correctors, and in parallel when the solver runs in parallel.
  • Function objects are switched off (-noFunctionObjects) and the pressure is not written, so the solver starts from the initial pressure.

A potential flow has no separation and no jets, but its mass flux is correct everywhere. This shortens the first iterations of the solver and makes the start more robust.

Equations

∇2Φ=∇⋅ϕ∗\nabla^2\Phi = \nabla\cdot\phi^{*}
(1)
ϕ=ϕ∗−(∇Φ)f⋅Sf,∇⋅ϕ=0\phi = \phi^{*} - \left(\nabla\Phi\right)_f\cdot\mathbf{S}_f, \qquad \nabla\cdot\phi = 0
(2)
wheremeaningunit
Φ\PhiVelocity potentialm²/s
ϕ∗\phi^{*}Face volume flux of the initial velocity fieldm³/s
ϕ\phiCorrected, divergence-free fluxm³/s
Sf\mathbf{S}_fFace area vectorm²

Default and rule

Default
on
Rule

On.

Source

Validation on case V1 (a 2.0 m multi-chamber muffler with a perforated pipe and three absorptive packings): with the inlet flux written as described above, the potential start reduced the pressure clipping of the compressible start-up from 3-4 iterations to one. It did not by itself stabilise SIMPLEC on that case. The potential-flow solver: (OpenFOAM user guide, 2026).

Valid range on | off

Choice

On or off. Switch it off only to test whether the initial field matters for a difficult start.

References 1

  1. OpenCFD Ltd. (2026). OpenFOAM user guide. openfoam.com. Web page