Vortex motion in the early stages of unsteady flow around a circular cylinder |
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Authors: | Guo-Can Ling Xie-Yuan Yin |
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Affiliation: | (1) Institute of Mechanics, Chinese Academy of Sciences, Beijing, China;(2) University of Science and Technology of China, Hefei, China |
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Abstract: | In this paper, processes in the early stages of vortex motion and the development of flow structure behind an impulsively-started
circular cylinder at high Reynolds number are investigated by combining the discrete vortex model with boundary layer theory,
considering the separation of incoming flow boundary layer and rear shear layer in the recirculating flow region. The development
of flow structure and vortex motion, particularly the formation and development of secondary vortex and a pair of secondary
vortices and their effect on the flow field are calculated. The results clearly show that the flow structure and vortices
motion went through a series of complicated processes before the symmetric main vortices change into asymmetric: development
of main vortices induces secondary vortices; growth of the secondary vortices causes the main vortex sheets to break off and
causes the symmetric main vortices to become “free” vortices, while a pair of secondary vortices is formed; then the vortex
sheets, after breaking off, gradually extend downstream and the structure of a pair of secondary vortices becomes relaxed.
These features of vortex motion look very much like the observed features in some available flow field visualizations. The
action of the secondary vortices causes the main vortex sheets to break off and converts the main vortices into free vortices.
This should be the immediate cause leading to the instability of the motion of the symmetric main vortices. The flow field
structure such as the separation position of boundary layer and rear shear layer, the unsteady pressure distributions and
the drag coefficient are calculated. Comparison with other results or experiments is also made.
This work was presented at the First Asian Congress of Fluid Mechanics, Bangalore in December 1980. |
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Keywords: | vortex motion unsteady flow circular cylinder flow structure boundary layer separation rear shear layer separation viscous vortex core |
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