Low frequency wake dynamics of cantilevered circular cylinders at an aspect ratio of 4

Near-wake characteristics of a low aspect ratio (h=d = 4) cantilevered circular cylinder protruding a thin laminar boundary layer have been investigated both experimentally (Re = 10;400) and numerically (Re = 300). Despite the substantial differences in the investigated Re, the unsteady wake topology exhibits similar instability mechanisms: (i) a Karm an-like vortex shedding instability, and (ii) a low- frequency instability which manifests as a coupling between the flow over the free end and the base flow near the cylinder-wall junction. Attention is drawn to the lowfrequency instability, which comprises a significant portion of the kinetic energy content in the wake, and has not been reported in previous experimental or numerical investigations. It appears to be characteristic of intermediate aspect ratio cantilevered circular geometries.