wallfunction
A wallfunction is a semi-empirical relation used in computational fluid dynamics to model the near-wall region of turbulent flows without resolving the viscous sublayer. It provides a link between velocity, distance from the wall, and wall shear stress, delivering a boundary condition that replaces the need for very fine near-wall grids in many simulations.
In the typical formulation, dimensionless wall variables are used: y+ = ρ uτ y / μ and u+ = u / uτ,
There are several variants. Standard (equilibrium) wall functions assume a fully turbulent, attached boundary layer and
Limitations include reduced accuracy in flows with strong adverse pressure gradients, flow separation, reattachment, high-pressure or