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Title: Transient behavior of vortical flow through a constant diameter pipe

Description: This video shows the transient behavior of a dye filament introduced close to the axis of symmetry of a vortex when the vortex is subject to a sudden increase in swirl. The apparatus consists of a conventional guide vane arrangement to generate the swirl and a constant diameter pipe through which the vortex flows. The swirl intensity is determined by the angle of attack of the guide vane, ß. The Reynolds number (based on the pipe diameter and the bulk axial velocity) is constant and approximately equal to 4000.

The video shows the evolution of an almost axisymmetric ringlike structure when ß and the increment ∆ß are 26" and 2.2", respectively. Note that ∆t is the time measured from the first frame shown and that the flow is from left to right. For sufficiently small values of ß, or small increments ∆ß, the disturbance decayed and was swept out of the apparatus.

When ß or ∆ß were sufficiently large, the ringlike structure grew and the number of internal turns increased until it developed a periodic, nonaxisymmetric wobble. The amplitude of this wobble increased until the filament of dye assumed a distinct spiral shape. For example, when ß and ∆ß were 26" and 2.8", respectively, the spiral disturbance was swept out of the apparatus or, when ß was sufficiently large, eventually meandered very slowly about an equilibrium position within the pipe. As ß was further increased, the equilibrium position of the spiral moved upstream, its pitch decreased, and the rate of rotation increased.

Credits: T. W. Mattner, M. S. Chong, and P. N. Joubert


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Contributed By: Tausif Billah

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