On the vortex dynamics in the wake of a finite surface-mounted square cylinder |
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Authors: | P?Sattari J?A?Bourgeois Email author" target="_blank">R?J?MartinuzziEmail author |
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Institution: | (1) Department of Mechanical and Manufacturing Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 1N4, Canada |
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Abstract: | The shedding process in the near wake of a surface-mounted, square cross-section cylinder of height-to-width aspect ratio
4 at a Reynolds number of 12,000 based on free-stream velocity and the obstacle width was investigated. The boundary layer
thickness was 0.18 obstacle heights based on 99% free-stream velocity. The study is performed using planar high frame-rate
particle image velocimetry synchronized with pressure measurements and hot-wire anemometry. Spatial cross-correlation, instantaneous
phase relationships, and phase-averaged velocity data are reported. Two dominant vortex-shedding regimes are observed. During
intervals of high-amplitude pressure fluctuations on the obstacle side faces, alternate formation and shedding of vortices
is observed (regime A) similar to the von Kármán process. Regime B is characterized by two co-existing vortices in the obstacle lee throughout the shedding cycle and is observed within low-amplitude
pressure fluctuation intervals. Despite the coexisting vortices in the base region, opposite sign vorticity is still shed
out-of-phase downstream of this vortex pair giving rise to a staggered arrangement of counter-rotating vortices downstream.
While the probability of occurrence of Regime B increases toward the free end, the amplitude modulation remains coherent along the obstacle height. Conditionally phase-averaged
reconstructions of the flow field are consistent with the spatial distribution of the phase relationships and their probability
density function. Earlier observations are reconciled showing that the symmetric shedding of vortices is a rare occurrence. |
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