Convoluted diffuser

A conduit for carrying a fluid in a downstream direction and having wall means defining the internal flow surface of said conduit, said conduit including an upstream portion having means defining an outlet end with a first cross-sectional flow area, a downstream portion having means defining an inlet end of second cross-sectional flow area larger than said first cross-sectional flow area and spaced downstream from said upstream portion outlet end, and a diffuser section disposed between said upstream portion and downstream portion, wherein said internal flow surface comprises a surface of said diffuser section joining said outlet end and said inlet end, wherein said diffuser section surface joining said inlet end and outlet end comprises a plurality of adjacent, adjoining, alternating troughs and ridges extending downstream to said downstream portion inlet end, at least one of said plurality of troughs being disposed between and defined by an adjacent pair of said ridges, said plurality of troughs and ridges increasing in depth and height, respectively, in the downstream direction and having maximum depth and height at said inlet end, said diffuser section gradually increasing in cross-sectional flow area in the downstream direction, and wherein said conduit has means defining a substantially stepwise increase in cross-sectional flow area at said inlet end of said downstream portion wherein said plurality of troughs and ridges are sized and contoured to generate pairs of adjacent, large-scale counterrotating vortices, each vortex rotating about axes extending substantially in the downstream direction.

A device for carrying a fluid in a downstream, principal flow direction, comprising wall means defining a diffusing section for decreasing the velocity in the principal flow direction and increasing pressure, said diffusing section having means defining an inlet and an outlet, the inlet cross-sectional flow area being less than the outlet cross-sectional low area, said diffusing section wall means having a fluid passage defining surface extending from said inlet to at least said outlet, said surface having formed therein, between said inlet and outlet, a plurality of downstream extending, adjoining alternating troughs and ridges, both being U-shaped in cross-section taken perpendicular to the principal flow direction, including at least one pair of adjacent ridges defining one of said troughs therebetween, said plurality of troughs each having a downstream end, the depth and height of said plurality of troughs and ridges both increasing in the downstream direction from an initial depth and height, respectively, of zero, said plurality of troughs and ridges having their maximum depth and height, respectively, at said downstream ends of said plurality of troughs, wherein adjoining troughs and ridges blend smoothly with each other along the length thereof forming a smoothly undulating surface, wherein said plurality of troughs and ridges are sized and contoured to generate pairs of adjacent, large-scale counterrotating vortices, each vortex rotating about axes extending substantially in the downstream direction, said fluid passage defining surface immediately upstream of and adjacent said plurality of troughs and ridges being configured to avoid streamwise, two-dimensional boundary layer separation from said passage defining surface during operation of said device, and wherein each of said plurality of troughs comprises a pair of downstream extending sidewalls facing and substantially parallel to each other over the length of each said trough.