Unsteady three-dimensional wake structure behind magnetically levitated freestream-aligned circular cylinder

In the present study, unsteady three-dimensional wake structures behind a freestream-aligned circular cylinder were investigated. The ventilation tests were performed without the support interference using the 0.3-m magnetic suspension and balance system (MSBS). Cylindrical models with fineness ratios of 1.0, 1.5, and 2.0 were used for the tests. The Reynolds numbers based on the model diameter were 3.3×10^4 and 6.7×10^4. The velocity fields on the plane perpendicular to the central axis of the cylinder were measured using stereo particle image velocimetry (PIV). The time-averaged velocity in the freestream direction at 1.0D from the cylinder base shows an axisymmetric distribution. Instantaneous wake position was calculated and it shows that the position randomly fluctuates in the plane. In addition, a frequency analysis using fast Fourier transformation was applied and the characteristic fluctuations of the velocity was investigated. The wake structures of the recirculation bubble pumping and the large-scale vortex shedding were clarified from the results.