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標題: Characteristics of Recirculation Zone Structure behind an Impulsively Started Circular Cylinder
作者: Lin, C.
Hsieh, S.C.
Lin, W.J.
Raikar, R.V.
關鍵字: Impulsively started cylinder
Recirculation zone
Negative velocity
Similarity profile
Similarity of geometric shape
lattice-boltzmann method
feeding mechanism
unsteady flows
early stage
期刊/報告no:: Journal of Engineering Mechanics-Asce, Volume 138, Issue 2, Page(s) 184-198.
摘要: The characteristics of the recirculation zone structure behind an impulsively started circular cylinder for Reynolds number R-e ranging from 500 to 2,000 and nondimensional time T ranging from 0.5 to 5.0 are investigated experimentally using particle image velocimetry (PIV) and flow visualization techniques. On the basis of the flow visualization pictures and velocity maps, both obtained by a reference frame with a moving coordinate system, the evolution of the recirculation zone structure is studied with special emphasis on the negative velocity subzone. The negative velocity subzone is enveloped by the boundary consisting of the zero-velocity points inside the recirculation zone, and the streamwise velocity profile inside and near the negative velocity subzone is characterized by a jetlike flow moving toward the cylinder. During the evolution of the recirculation zone, the representative dimensions of the vortical structure both in the streamwise and vertical directions, including the recirculation zone length and the center-to-center distance between two primary vortex cores, are found to increase rapidly with time. Characteristic length and velocity scales are proposed first in the literature not only to demonstrate the similarity profile for streamwise velocity within and near the negative velocity subzone, but also to exhibit the similarity for geometric shape of the negative velocity subzone via the ratio of the width of the negative velocity subzone (i.e., the vertical distance between two zero-velocity points) to the center-to-center distance between two primary vortex cores. The very important observation is that the similarities of velocity profile and geometric shape represent promising self-preservation for the jetlike flow enclosed by the zero-velocity points forming the boundary of the negative velocity subzone. In addition, time variation of the nondimensional circulation of two primary vortices in the recirculation zone is studied and found to increase with an increase in the nondimensional time. DOI: 10.1061/(ASCE)EM.1943-7889.0000314. (C) 2012 American Society of Civil Engineers.
ISSN: 0733-9399
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