Advection schemes

Vanellus exposes advection schemes for momentum, energy, turbulent kinetic energy (tke), and specific dissipation rate (sdr). Pressure has no advection scheme.

Bounded advection

All public API advection choices use the bounded form of the advective operator. Vanellus retains both terms in

\[ (\mathbf{J}\cdot\nabla)\phi = \nabla\cdot(\mathbf{J}\phi) - \phi \nabla\cdot\mathbf{J}. \]

including while the iterative face flux is not yet exactly divergence-free. This behavior is always enabled and is not an API option.

Here, bounded describes the operator formulation; it is not a selectable flux limiter and does not guarantee that a second-order solution cannot overshoot or oscillate.

First-order upwind

upwind uses the upstream cell value at each face. It is robust and adds numerical diffusion, particularly where the flow crosses cells obliquely or the mesh is too coarse to resolve a gradient.

The standard numerics presets use first-order upwind for every advected equation. It is the recommended starting point because it separates basic case stability from the additional sensitivity of a higher-order reconstruction.

Second-order upwind

second_order_upwind applies a linear-upwind correction calculated from the previous iteration’s field gradient. It can reduce numerical diffusion on a suitable mesh, but the explicit correction makes the coupled iteration less stable and more sensitive to mesh quality.

See also

• Numerics presets shows the advection choice shared by the standard presets.
• Return to first-order advection applies this change to an unstable field.
• Relaxation explains the separate controls used to damp iterative updates.
• API reference lists exact configuration fields and limits.