abl

Friction velocity in m/s. Must be positive when set. The compressible solver needs friction_velocity, surface_layer_height or both.

Height of the surface layer (m) that the log-law profile applies within; above this height the profile is clamped. C++ sentinel default is -1.0 (unset): the compressible read sites then derive it from roughness_length and friction_velocity when both are set.

Monin-Obukhov stability length L (m). Negative values are read as unstable and add a stability correction to the log-law velocity/TKE/epsilon (only when L < 0 — the current C++ never applies a correction for L > 0, i.e. stable stratification is not represented here). Zero is not a valid value. The solver's local default is +1.0 (a positive, 'no correction' value) when the key is absent — this is the effective neutral default. Leave unset for neutral stability.

Reference turbulent kinetic energy (m^2/s^2), scaled by friction_velocity**2 to give the profile's TKE. Only applied when friction_velocity is also set — if friction_velocity is absent, the solver discards this value with a warning and derives TKE from the wall distance instead.

Unit vector [x, y, z] defining the vertical ('up') direction used with ground_level to compute height above ground as dot(position, up) - ground_level. Default when unset is (0, 0, 1).

Datum elevation of the ground (m) in the mesh's own coordinate system, measured along 'up'. Subtracted from dot(position, up) before the log-law height is computed, as height = min(dot(p, up) - ground_level, surface_layer_height) — it shifts where the profile's height origin sits, it is NOT a measurement or reference height. This is unrelated to the aerodynamic roughness length z₀ (that's 'roughness_length' above) and unrelated to ABLZone.reference_height. NOTE: the initial-condition profile reads this key but never applies it to the initial field — only the farfield BC profile honours it — so a mesh with a non-zero ground datum gets inconsistent IC/BC profiles.