Round Sudden-Expansion Flows

Abstract

This paper describes an experimental investigation of the water flows through one axisymmetric and two asymmetric round sudden expansions from a 48 mm to an 84 mm diameter pipe and eccentricities of the pipe axes of 0, 5 and 15 mm respectively. Flow visualization revealed the presence of vortex rings downstream of the plane of expansion for transitional Reynolds numbers (Re, based on the upstream pipe diameter and bulk flow velocity) and reattachment lengths were determined in the Reynolds number range 120–40 000 for all three cases. Detailed measurements of the three mean velocity components and corresponding fluctuations were obtained by laser anemometry for Re = 40000. Wall static pressure measurements are also presented. The results show that asymmetry of the inlet geometry strongly influences the distribution of mean and turbulence quantities downstream of the expansion and results in three-dimensional reattachment. In all three flows, the mean flow was nearly uniform and the turbulence nearly homogeneous at distances of seven diameters of the large pipe downstream of the expansion. Higher levels of turbulence were found in the asymmetric ducts with maxima twice those in the axisymmetric duct.