The Wall node sets a slip wall condition for the fluid. This prescribes a no-penetration condition, u·n = 0.

The Normal wall velocity setting controls the normal wall velocity Ubnd. The list is per default set to Automatic from frame. The physics automatically detects if the spatial frame moves. This can for example happen if an ALE interface is present in the model component. If there is no movement Ubnd = 0. If the frame moves, Ubnd becomes equal to the frame movement projected on the wall normal. Ubnd is accounted for in the actual nonpenetration boundary condition prescribed, so that u ⋅ n = Ubnd.

Select Zero (Fixed wall) from Normal wall velocity selection list to always prescribe Ubnd = 0.