An experimental study of round sudden-expansion flows

This paper describes an experimental investigation of the flows through one axisymmetric and two asymmetric round sudden expansions with area ratios of 3.06 and eccentricities of the pipe axes of 0, 5 and 15mm respectively. Flow visualization revealed the presence of vortex rings downstream of the plane of expansion for transitional Reynolds numbers (Re) only. Reattachment lengths were determined for Re in the range 120 to 40,000 for all three cases. The results show that asymmetric inlet conditions influence strongly the distribution of mean and turbulence quantities downstream of the expansion and result in three-dimensional reattachment. In all three flows, the mean flow was nearly uniform and the turbulence nearly homogeneous at distances of 7 diameters of the large pipe downstream of the expansion. Higher levels of turbulence were found in the asymmetric ducts with maxima of 0.05 sqm/sq s, twice those in the axisymmetric duct.