Nonstationary, Three-Dimensional Aspects of Flow Around Circular Cylinder at Critical Reynolds Numbers

Nonstationary three-dimensional aspects of flow around a smooth circular cylinder at Reynolds numbers of 3.4-3.9 x 10(5) were examined with pressure measurements on the cylinder over a spanwise region of two diameters of the cylinder, and a hot-wire probe fixed in the near-wake region. The real-time signals measured showed that the flow behaviors were critically affected by the presence of separation bubble, which could be seen intermittently within a limited spanwise extent on the cylinder. Further, it is noted that physical interpretation's based on the time-mean measurement results could be misleading. Rather, in this study a nonstationary data analysis technique was introduced to resolve the vortex shedding frequency in the instantaneous sense. The results obtained lead to further insights into the instantaneous flow characteristics in the critical regime.