Abstract
Wall blocking is an inviscid mechanism due to imperviousness of the boundary and is believed to act over distances farlarger than the viscous length scale. In recent years this property is being introduced to model wall turbulence moreprecisely and efficiently. Nonetheless no general agreement on the basic concepts, especially at later times after theboundary insertion to the flow, has been reached so far. Here a discussion is conducted based on recent DNS/LES resultsof fully-developed closed/open-channel flows, especially about the extent to which the blocking effects are observednear an impermeable surface (i. e. solid wall or ideal free surface). Near a solid wall the extent does scale on the viscousscaling law while an outer scale (water depth) controles the extent near a free surface. Various unresolved issues arealso discussed, mostly owing to a lack of reliable DNS database at high Reynolds numbers.
