An experimental/numerical study of 3-d flow past double-sided expansions

The effect of three-dimensionality on low Reynolds number flows past a symmetric sudden expansion in a duct was investigated. The upstream flow was fully developed for a 1:2 expansion with 1:6 aspect ratio. Reynolds numbers in the range of 150 to 600 were experimentally investigated using particle image velocimetry to obtain whole field data at various planes in the duct. Side-wall proximity was found to enhance flow stability, helping sustain flow symmetry to higher Reynolds numbers in comparison to nominally two- dimensional double-expansion geometries, which were investigated numerically. The geometric characteristics of the expansion were completely captured using an effective expansion ratio term, which was shown to scale the critical Reynolds number marking the occur- ance of bifurcation. In addition, the velocity profiles determined from two-dimensional simulations using the effective expansion ratio agreed well with the measured profiles.