Vortical Structures in the Corner Region of a Turbulent Square-Duct Flow.

Abstract

Vortical structures in the corner region of a fully developed turbulent square-duct flow have been identified at low Reynolds number Re=7000 by using conditionally sampling data obtained from two-point LDV measurements. A single quasi-streamwise vortex is found to be located roughtly on the corner bisector in the vicinity of a duct corner in a statistical sense. Its diameter and circulation scaled in wall units are shown to be similar to those of a streamwise vortex in canonical near-wall turbulence. The generation process of Reynolds stresses in the corner region is interpreted in terms of quasi-streamwise vortical motion. This vortical motion greatly contributes to the transfer of the streamwise momentum in the cross-flow direction between two walls adjacent to the corner, so that the flows on the two walls strongly interact with each other and the interaction involves a significant difference in Reynolds stress generation from near-wall turbulence. The spatial distributions of fluctuation velocity, streamwise vorticity and Reynolds stresses are presented in the corner region to discuss the flow structure induced by the quasi-streamwise vortex.