Permanent three-dimensional patterns in turbulent flows with essentially two-dimensional wall configurations

The phenomenon of steady three-dimensional structures transverse to the main Bow direction in turbulent Bows with mainly two-dimensional wall configurations has been investigated. Time invariant two-dimensional temperature distributions in an asymmetrically ribbed channel have been detected by infrared thermography and are compared with published data of three-dimensional Row structures in turbulent boundary layers above a single rectangular cavity and a single rib inside a turbulent channel flow, respectively. The periodic length of the observed Bow structures correlate quite well among different investigations, although methods of investigation and boundary conditions are different. It can be concluded that such structures in turbulent flows with nearly two-dimensional boundary conditions (large aspect ratio of the cross-section) are self-sustaining flow effects. No physical explanation of the origin of this phenomenon and of the observed dependencies on the wavelength are available yet.