The effect of spatial restriction on the inner-layer structure of wall turbulence

Abstract

Hot-film-anemometer measurements were carried out in a shear flow between a flat plate and a moving plate fitted with an array of tall fences. The effect of spatial restriction by the fences on the inner-layer structure of the boundary layer developing on the flat-plate side was investigated. It was revealed that the inner-layer structure was maintained even when the tips of the fences were passing at a distance y+ = 45 from the flat plate; the flow did not become laminar-like until the tips reached y+ = 25. These results suggested the physical view that the inner layer of wall turbulence has a tough, self-sustaining structure, which is uniquely determined under a given mean wall shear stress and is hardly influenced by outer-layer disturbances provided that its own spatial extent of about 45 ν/u* from the wall is maintained.