円柱の伴流渦に関する実験的研究(第1報)風胴壁面に沿う境界層による影響

抄録

When a circular cylinder is supported through both side walls of a wind tunnel, the effects of the boundary layers along the side walls on the wake of the cylinder in a uniform flow were investigated in the pure Karman-vortex range of Reynolds number.
When the boundary layers are cut off from the uniform flow passing the cylinder by two small circular plates attached to each end of the cylinder, the behaviours of the vortex shedding can be classified into two modes by the Reynolds number. Namely, in the range of Re≤160, i.e., the regular mode, the regular vortex shedding takes place uniformly in the axial direction of the cylinder, and the Karman-vortex street is formed in the wake. The primary Karmanvortex street is deformed as the distance from the cylinder is increased. Farther downstream in the wake, however, it tends to rearrange itself again into a configuration of the Karman-vortex street on a larger scale than that of the primary one. In the range of Re>160, i.e., the irregular mode, the turbulent velocity fluctuations are observed in the wake. The rearrangement of vortices in the wake can not be observed.
On the other hand, when that end of the cylinder which has no circular plate is immersed in the boundary layer on a wall. the vortex shedding is affected by the boundary layer so that two more transitions between the regular and irregular mode appear in the range of Re≤160, The transition Reynolds numbers depend on the distance from the wall. No rearrangement into the secondary Karman-vortex street is seen in the regular mode. The flow in the rangeof Re>160 has always the irregular mode.