Bluff-body vortex shedding with focus on the turbulent wake of finite surface-mounted square cylinders at moderate Reynolds numbers is studied experimentally using particle image velocimetry (PIV) and hotwire anemometry (HWA). Emphasis is put on understanding the formation and growth process of vortices, their interaction and separation from the feeding shear layer.
The conventionally described vortex shedding process is reassessed. It is concluded that contrary to the traditionally proposed mechanism, the mutual interaction between counter-rotating vortices is not the cause for the limit to vortex growth. Rather, the vortex growth is naturally limited and the feedback from the shed vortices serves to lock-in the shedding frequency. Furthermore, based on observation of the shedding of an isolated two-dimensional vortex, a length scale defined as the distance between the shear-layer edge and vortex center at the streamwise location of maximum vortex circulation is shown to result in a collapse of non-dimensional circulation. On the ground of scaling principles, this scale is shown to also result in a collapse of the shedding frequency.
This work also resolves an apparent discrepancy in the literature with respect to the existence of symmetric and anti-symmetric shedding regimes. Using spatial cross-correlation, instantaneous phase relationships, and phase-averaged velocity data obtained from PIV and HWA, it is shown that the shedding in the wake of surface-mounted finite square cylinders is predominantly anti-symmetric and thus consistent with the von Kármán process. What had been interpreted as symmetric shedding appears to be a distortion of the regular shedding process. During periods of low-amplitude fluctuations, two counter-rotating vortices exist concurrently in the base region. However, counter-rotating vortices are still shed alternately.