摘要
We visualized the wake structure of circular disks falling vertically in quiescent water. The evolution of the wake was shown to be similar to the flow patterns behind a fixed disk. The Reynolds number, Re = Ud/v, is in the range of 40 - 200. With the ascension of Reynolds numbers, a regular bifurcation occurred at the first critical Reynolds number Reel, leading to a transition from an axisymmetric wake structure to a plane symmetric one; A Hopf bifurcation took place at the second critical Reynolds number Rec2, as the wake structure became unsteady. Plane symmetry of the wake structure was first lost as periodic vortex shedding ap- peared, but recovered at higher Reynolds number. The differ- ence between the two critical Reynolds numbers was found to be shape-dependent, as we compared our results for thin discs with those for other falling bodies, such as spheres and cones. This observation could be understood in terms of the instability mechanism of the vortical structure.
We visualized the wake structure of circular disks falling vertically in quiescent water. The evolution of the wake was shown to be similar to the flow patterns behind a fixed disk. The Reynolds number, Re = Ud/v, is in the range of 40 - 200. With the ascension of Reynolds numbers, a regular bifurcation occurred at the first critical Reynolds number Reel, leading to a transition from an axisymmetric wake structure to a plane symmetric one; A Hopf bifurcation took place at the second critical Reynolds number Rec2, as the wake structure became unsteady. Plane symmetry of the wake structure was first lost as periodic vortex shedding ap- peared, but recovered at higher Reynolds number. The differ- ence between the two critical Reynolds numbers was found to be shape-dependent, as we compared our results for thin discs with those for other falling bodies, such as spheres and cones. This observation could be understood in terms of the instability mechanism of the vortical structure.
基金
supported by the National Natural Science Fundation of China (10910301062,11102197)
the National Climb-B Plan (2009CB724100)
the National Foundation for Distinguished Young Scholar of China (10525208)
the Science Fund for Creative Research Groups (10921202)
