Basic experiments were performed to investigate the use of vortex rings as a means to transport a small amount of fluid. The compact and unchanging nature of vortex rings is suitable to obtain high-density distribution of the transported fluid within a specific confined region. A certain amount of fluid in a cylinder was discharged into a quiescent fluid in the water tank by a piston through an orifice 20.0 mm in diameter. The fluid distributions transported by a set of 10 vortex rings, by 20 vortex rings, and by a single, short puff-like jet were quantitatively analyzed and compared. For all ejection conditions, the total volume of discharged fluid and the average ejection velocity through the orifice are the same (78.5×10 4 mm 3 and 125 mm/s, respectively). The particle count method was used to quantitatively measure the distribution of the transported fluid. As a result, the vortex rings were found to be superior to the single short discharge for transporting a fluid to obtain a high density distribution in a narrow region.
The process of the formation of a vortex street in the wake behind a fla t pia te set parallel to a uni form flow was investigated in a low speed wind tunnel. The vorticity distributions in the wake were calculated from the measured velocities using Taylor's hypothesis.Just behind the plate, the equi-vorticity lines were nearly parallel to the free stream. At locations somewhat downstream, sinusoidal contour lines appeared near the wake center. Further downstream. some closed contour lines appeared in the figures mapped. The arrangement of the closed lines suggests the existence of a vortex street. The maximum value for vorticity in a wave length of the fundamental velocity fluctuation decreased in the downstream direction; the concentration of vorticity, however, increased in a region the further downstream it was. Meanwhile, the value for circulation obtained by the surface integral of vorticity within the closed contours of a vortex increased until the vortex street was estahlished.
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