Dynamic shedding characteristics in the wake of vertical, surface mounted square and circular cylinders of aspect ratio (H/D) 0.5, 2, 4 and 8 are investigated using high frame-rate particle image velocimetry and thermal anemometry for Reynolds numbers, based on the obstacle width/diameter ranging between 6 × 103 and 105. The wavelet transform was used to determine the instantaneous phase relationship for either pressure or velocity fluctuations on opposite sides of the obstacles. Except for the smallest aspect ratio, two shedding modes with different vortex configurations are observed in the formation region: i) Alternate formation of vortices accompanied by high-amplitude fluctuation; ii) Events of simultaneous formation of two vortices resulting in low-amplitude activity and varying phase relationship between opposing sides. These counter-rotating coexisting vortices are generally shed alternately. In the case of aspect ratio 0.5 prism, periodic activity is irregular and the shedding behavior is different from higher aspect ratio bodies.

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