The quasi-periodic vortex shedding structure in the wake of finite surface-mounted square- and circular-cross-section cylinders is investigated for several aspect ratios. Complex continuous wavelet transforms (CWT’s) are used to obtain a phase function φ(t) from hot-wire measurements. Mean relative phases and phase averaged particle image velocimetry (PIV) measurements indicate an upstream bending of the initially vertical shed vortex structures for all obstacles investigated. This upstream bending mechanism reorients vorticity streamwise and is described in terms of Biot-Savart induction that occurs at the junction of the tip and side shear layers. This mechanism of vorticity concentration/reorientation is inherently three-dimensional and interacts with the nominally two-dimensional mechanism of alternate vortex sheet roll-up from the opposing obstacle side faces. This mechanism typically acts higher along the height for square-as opposed to circular-cross section cylinders and plays a more dominant role for smaller aspect ratios.

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