Vortical structures behind a sphere at subcritical Reynolds numbers

• Published in: Physics of fluids (1994) 2006-01, Vol.18 (1), p.015102-015102-14
• Main Authors: Yun, Giwoong, Kim, Dongjoo, Choi, Haecheon
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Fluid dynamics; Fundamental areas of phenomenology (including applications); Jets; Physics; Turbulence simulation and modeling; Turbulent flows, convection, and heat transfer; Wakes
• ISSN: 1070-6631; 1089-7666
• DOI: 10.1063/1.2166454

Large eddy simulations of turbulent flow over a sphere are conducted at subcritical Reynolds numbers ( Re = 3700 and 10 4 ) based on the freestream velocity and sphere diameter. At Re = 3700 , the separating shear layer persists downstream to form a cylindrical vortex sheet and its instability becomes manifest at x ≈ 2 d . The flow right behind the sphere contains only a few vortices. On the other hand, at Re = 10 4 , the shear-layer instability occurs right behind the sphere in a form of vortex rings, and the flow becomes turbulent in the near wake. Therefore, at Re = 10 4 , the size of the recirculation region is smaller and the wake recovers more quickly than at Re = 3700 . At both Reynolds numbers, large-scale waviness of vortical structures is observed in the wake and the plane containing the large-scale waviness changes quasirandomly in time. This waviness is more pronounced at Re = 10 4 than at Re = 3700 . The mechanism responsible for this large-scale waviness of vortical structures is shown to be closely associated with the temporal evolution of vortices generated by the shear-layer instability.