Experimental Studies of the Flow through an Axial Sudden Expansion with Orifice.

Separated and reattaching flows produced by an axial sudden expansion have been studied experimentally. The flow fields were produced by an axisymmetric sudden enlargement from an orifice of diameter 30mm to a pipe of diameter 80mm. Mean velocities and turbulent intensities were measured by a hot-wire anemometry. The Reynolds number based on the orifice diameter was 25, 000. Flow visualization tests were also done. It was shown that large-scale vortices are produced at the orifice. These vortices begin to pair each other, but soon they lose their axisymmetry, i.e. breakdown occurs. The streamwise position where this breakdown occurs is located at much more upstream position when compared with that of an orifice free-jet flow under the same inlet condition.