An experimental investigation was carried out to study the effect of the bluntness factor of a bluff body on the vortex shedding mechanism in the wake region. Experiments were carried out for a range of bluntness thicknesses. Particle image velocimetry (PIV), dynamic surface pressure and hotwire measurements were taken. PIV showed the bluntness thickness effect on the attachment of the generated vortex to the surface and on the formation length of the vortex. The tonal-coherence between hotwire measurements in the boundary layer upstream of the bluntness and the surface pressure, was shown to be related to downstream location of the vortex core in the time averaged flow field. Velocity fields obtained with PIV indicated a distancing of the vortex formation with increasing bluntness. The study proposes the existence of a critical bluntness value above which the vortex detaches from the bluntness surface and the boundary layer upstream thus produces a lower surface pressure. Below this value the vortex is closer to the blunt surface increasing the vortex interaction surface and the produced surface pressure. However, for smaller bluntness values the relative scaling down of the vortex dominates, introducing a smaller interaction region and lower surface pressure. Both surface pressure reduction schemes suggest effective aeroacoustic noise reduction potential.
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