Laminar flow past a sphere rotating in the transverse direction |
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Authors: | Dongjoo Kim |
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Affiliation: | (1) School of Mechanical Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk, 730-701, Korea |
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Abstract: | Laminar flow past a sphere rotating in the transverse direction is numerically investigated in order to understand the effect
of the rotation on the characteristics of flow over the sphere. Numerical simulations are performed at Re = 100, 250 and 300,
where the Reynolds number is based on the free-stream velocity and the sphere diameter. The rotational speeds considered are
in the range of 0 ≤ ω* ≤ 1.2, where ω* is the maximum velocity on the sphere surface normalized by the free-stream velocity. Without rotation, the flow past a
sphere experiences steady axisymmetry, steady planar-symmetry, and unsteady planar-symmetry, respectively, at Re = 100, 250
and 300. With rotation, however, the flow becomes planar-symmetric for all the cases investigated, and the symmetry plane
of flow is orthogonal to the rotational direction. Also, the rotation affects the flow unsteadiness, and its effect depends
on the rotational speed and the Reynolds number. The flow is steady irrespective of the rotational speed at Re = 100, whereas
at Re = 250 and 300 it undergoes a sequence of transitions between steady and unsteady flows with increasing ω*. As a result, the characteristics of vortex shedding and vortical structures in the wake are significantly modified by the
rotation at Re = 250 and 300. For example, at Re = 300, vortex shedding occurs at low values of ω*, but it is completely suppressed at ω* = 0.04 and 0.6. Interestingly, at ω* = 1 and 1.2, unsteady vortices are newly generated in the wake due to the shear layer instability. The critical rotational
speed, at which the shear layer instability begins to occur, is shown to be higher at Re = 250 than at Re = 300.
This paper was recommended for publication in revised form by Associate Editor Dongshin Shin
Dongjoo Kim is an associate professor in the School of Mechanical Engineering at Kumoh National Institute of Technology. His research
interests include computational fluid dynamics, bluff-body wakes, and control of turbulent flows. He has a PhD in mechanical
engineering from Seoul National University. He is a member of the American Physical Society and the American Institute of
Aeronautics and Astronautics. |
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Keywords: | Sphere Wake Transverse rotation Vortex shedding Shear layer instability |
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