Measurement of turbulent flow in a square duct with roughened walls on two opposite sides

Abstract

A fully developed turbulent flow along a square duct, two opposite walls of which had been roughened by square cross-sectioned ribs, was measured with a hot-wire anemometer. This paper presents the resulting velocities and stresses and compares them with measurements taken in a square duct with four smooth walls. Symmetrical results, with respect to the axes of symmetry of the duct cross section, were obtained in every measured quantity. Terms on both sides of the vorticity transport equation were calculated, and the balance of terms was discussed. As is well known, smooth-walled square ducts yield two secondary flow cells in any given quadrant of a cross section. But in ducts whose opposite walls have been roughened, we found a hitherto unobserved phenomenon: only one relatively large cell appeared in each quadrant of a duct's cross section.