Fully Developed Turbulent Flows through Rectangular Ducts with One Roughened Wall

Abstract

An experimental study has been conducted on fully developed turbulent flows through rectangular ducts with one rough wall. Two ducts, one with a long-side rough wall and the other with a short-side rough wall, have been used. The distributions of the mean velocities and turbulent stresses over a whole cross section in the fully developed region were measured by hot-wire anemometry. The secondary flow distributions in both the rough ducts were remarkably different from those in the smooth-walled duct. In the long-side rough duct, only one large secondary flow vortex appeared near the short-side wall. In the short-side rough duct, a similar large longitudinal vortex also appeared near the corner formed by the rough and the smooth walls. Furthermore, it was revealed that the contribution of turbulent shear stress <u₂u₃>^^^- was as important as that of the turbulent normal stresses (<u²₂>^^^--<u²₃>^^^-) for the generation of the secondary flow of the second kind in both the rough ducts.