円柱の伴流渦に関する実験的研究 (第2報)

カルマン渦列の再配列

抄録

The behavious of the wake in the pure Karman vortex street are divided into two classes in terms of Reynolds number. Namely, in the range of Re≤160, after the primary Karman vortex street is deformed at some distance downstream, the vortices in the wake tend to rearrange itself again into the secondary Karman vortex street. On the other hand, in the range of Re>160, the rearrengement of the vortices in the wake can not be observed.
The smoke-filament methods were used to visualize the flow pattern. On the photographs of the wake, the streamwise distances between the neighbouring vortices in the primary and the secondary Karman vortex street were measured respectively at the Reynolds numbers lower than 160. The ratio of the distance in the secondary Karman vortex street to that in the primary one is inversely proportional to the Reynolds number. The tendency is similar to that in the TANEDA'S experiment. At the same Reynolds number, however, the values of the ratio are much larger than that of TANEDA'S results.
The frequency, the wave form, the autocorrelation and the spectrum of the velocity fluctuations in the wake were measured by the hot-wire technique. The velocity fluctuations indicate regular sinusoidal waves and the frequency of the velocity fluctuations is constant both in the primary and the secondary Karman vortex street. The dimensionless frequency F=fdd²/ν is proportional to the Reynolds number, and the plotted lines for both vortex strees are parallel to each other, though the frequencies of the secondary Karman vortex street are smaller than those of the primary one.