The Coherent Structure of a Turbulent Boundary Layer over a d-Type Rough Surface at a Low Reynolds Number : Analysis with the Four Quadrant Method

Abstract

Quadrant analysis has been used to investigate the events contributing to Reynolds shear stress in the turbulent boundary layer over a d-type rough surface at a low-Reynolds number. By partitioning the stress into ejections, sweeps, and inwards and outward interactions, it was shown that the second quadrant, namely the ejection phase was the dominant event contributing to the stress through most of the boundary layer. Compared with the turbulent boundary layer over both a k-type rough surface and a smooth wall, the ratio of the fractional contributions of the second quadrant phase to the stress to that of the fourth quadrant one, and the ratio of the mean periods of those occurrences evaluated for a present wall flow were found to differ significantly. There existed a little correspondence between VITA events and the second and fourth quadrant type of events detected with the uv quadrant method.