Modification of the large-scale features of high Reynolds number wall turbulence by passive surface obtrusions

Abstract

A high Reynolds number boundary-layer wind-tunnel facility at New Mexico State University was fitted with a regularly distributed braille surface. The surface was such that braille dots were closely packed in the streamwise direction and sparsely spaced in the spanwise direction. This novel surface had an unexpected influence on the flow: the energy of the very large-scale features of wall turbulence (approximately six-times the boundary-layer thickness in length) became significantly attenuated, even into the logarithmic region. To the author's knowledge, this is the first experimental study to report a modification of 'superstructures' in a rough-wall turbulent boundary layer. The result g..