Turbulent flow through a rectangular duct with one roughened long-side wall

An experimental study was conducted on a fully developed turbulent flow through a rectangular duct of aspect ratio 2:1, one of whose long-side walls was roughened. Detailed and reliable results of such quantities as the secondary-flow velocities and the turbulent shear stresses were obtained by using a well-devised technique of the hot wire anemometry developed by the authors. The secondary-flow pattern in the rough duct was remarkably different from that in the smooth duct. Only one large longitudinal vortex appeared in the vicinity of each short-side wall. On the other hand, in quite a large region near the core, the secondary-currents proceeded from the smooth long-side wall to the rough one along the midplane of the rough wall. Furthermore it was found that the production and convection terms in the vorticity equation, which had been believed to balance, did not balance in the rectangular rough duct.