The wall boundary condition would be applied to an external face or surface.
The flow velocity at the wall can be described by the following types:
Additionally, to generate the boundary layer profile near wall regions, two approaches are available:
Appropriate functions are used to model the velocity profile. Thus, the boundary layer profile is not completely calculated and a relatively coarse mesh can be used near wall regions.
When using ‘Wall-function’, to achieve good accuracy, the y-plus for the first grid point must be in range
In this case no functions are used and the profile is completely resolved. For this approach the mesh has to fulfill certain criterion and should be particularly of high resolution near wall regions.
For 'Full Resolution' Y+ should be smaller than 1. This is highly recommended to capture the correct flow physics.