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Turbulence and Shear Flow Phenomena -1 First International Symposium

ISBN:
1-56700-135-1 (Print)

LONGITUDINAL AND SPANWISE STRUCTURES IN A TURBULENT WAKE

H. J. Zhang
Department of Mechanical Engineering The Hong Kong Polytechnic University Hung Horn, Kowloon, Hong Kong

Yu Zhou
Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

Robert Anthony Antonia
Discipline of Mechanical Engineering, University of Newcastle, Newcastle, 2308, NSW, AUSTRALIA

Abstract

Approximations to the three vorticity components ωx, ωy and ωz have been simultaneously obtained using a combination of four X-wires in the near-wake of a circular cylinder. The present objective is to investigate the likely spatial relationship between longitudinal and spanwise vortical structures. Conditional distributions of ωx, and ωy, based on detections of spanwise structures, indicated that the longitudinal structures are located upstream of the saddle point. The angles of the vorticity vector suggest that the most likely inclination, to the x-axis, of longitudinal structures is about 50°, aligned with the diverging separatrix between two consecutive spanwise structures. About 40% of ωx2, and ωy2, occur within the spanwise vortical structures, apparently resulting from the three-dimensionality of the structures, while the non-vortical regions account for 60%, which is largely attributed to the longitudinal structures. Spanwise structures also account for about 60−80% of ωz2.