Measurements of secondary flow in the boundary layers of a 180 degree channel

Abstract

Secondary flow measurements have been made within the turbulent boundary layers at two streamwise cross-sections of a 180 degree curved channel. The results indicate substantial three-dimensionality on all four walls of the channel. The secondary flows on the flat and convex surfaces are in accordance with those expected from considerations of the action of the centrifugal pressure gradients on the flat surfaces, while those on the concave surface appear to be dictated both by this effect as well as by the occurrence of longitudinal instability vortices. Some attempts have been made to reduce the cross-flows on the curved surfaces so that the influence of streamwise surface curvature on nominally two-dimensional turbulent boundary layers can be investigated.