An investigation into the effects of highly directional surface roughness on turbulent boundary layers

Abstract

The development of a zero pressure gradient turbulent boundary layer over a diverging and converging riblet arrangement is investigated experimentally. Such surface patterns are inspired by the very interesting work of Koeltzsch et al (6). Hot-wire studies show that these small, highly-ordered surface roughness patterns impose a high degree of three-dimensionality onto the boundary layer, causing a 100% variation in boundary layer thickness across the spanwise wavelength of the surface pattern (this, despite the fact, that the roughness height is less than 1% of the unperturbed boundary layer thickness). Detailed boundary layer traverses reveal that the local velocity above the diverging reg..