Turbulent Boundary Layer Flow Through a Gap in a Wall Mounted Roughness Element

The center-line development of a turbulent boundary layer flow through a gap in an isolated wall mounted roughness element has been studied experimentally. The centerline flow downstream of the gap can be divided into a distortion region followed by a readjustment region. The nature of the distortion produced by the gap varies with gap size and thus flows downstream of large gaps were found to differ significantly from those through small gaps. After distortion the layer readjusts itself and approaches equilibrium conditions of an undisturbed zero pressure gradient layer. The readjustment starts near the wall with the turbulence adjustment preceding the mean flow adjustment. For flow through all six gap sizes the growth of the centerline internal layer can be described by a single function if internal layer height and distance from the gap are non-dimensionalized with the local wall length scale. Well downstream of the gap it is shown that all six centerline flows are similar and are approaching equilibrium conditions in a similar manner.