Wall Model

The WallModel block configures the near-wall closure used by IBM wall boundaries. It controls the type of wall model, the nondimensional sampling used internally, optional transition sensing, and a lightweight solver cadence knob.

All values are interpreted in the global unit system.

Structure

WallModel
{
    variant         = "<algebraic | ode | none>"
    wall_spacing    = <number>                 # nondimensional (scaled by IBM.sample_dist_wm)
    temperature_bc  = "<adiabatic | number>"   # "adiabatic" or an isothermal wall temperature (e.g., 300)

    Transition
    {
        enable_sensor = <true|false>
        threshold     = <number>
    }

    Settings
    {
        solve_skip = <integer>
    }
}

Fields

• variant — selects the wall-model implementation:

  • "algebraic" — algebraic (one-point) wall model.
    • Temperature BC: forced to adiabatic (any temperature_bc value is ignored).
  • "ode" — ODE-based wall model (integrated profile).
    • Temperature BC: supports both adiabatic (temperature_bc = "adiabatic") and isothermal (temperature_bc = <number>).
  • "none" — disables wall modeling; wall BC behavior is determined solely by the chosen surface BC.

• wall_spacing — nondimensional wall distance used by the model and extrapolation logic.
  It is nondimensionalized by the IBM wall-model sampling distance (IBM.sample_dist_wm).

Wall Spacing in the Wall Model

It's recommended to set this to 0.001 and forget about it.

• temperature_bc — thermal boundary condition for the wall model:
  • "adiabatic" — adiabatic wall (no heat flux through the wall).
  • <number> — isothermal wall temperature (e.g., 300).
  • Note: If variant = "algebraic", the wall model is automatically adiabatic regardless of this setting.

Transition

The Transition sub-block controls a simple transition sensor gate for activating wall-model behavior:

• enable_sensor — when true, the wall model uses a sensor to decide whether to apply turbulent wall flux.
• threshold — sensor threshold for activation. Lower values trigger earlier. Value should be approximately 1.0.

Settings

• solve_skip — apply the wall-model every N steps (simple substepping throttle).
  solve_skip = 1 means run the wall-model every step; larger values reduce cost at the risk of lag.

Example

WallModel
{
    variant         = "algebraic"
    wall_spacing    = 0.001
    temperature_bc  = "adiabatic"

    Transition
    {
        enable_sensor = false
        threshold     = 0.1
    }

    Settings
    {
        solve_skip = 1
    }
}