The flow around square-based, wall-mounted pyramids in thin and thick boundary layer was experimentally investigated as a function of the pyramid apex angle, ζ, and, angle of attack, α, based on mean flow surface patterns, pressure and velocity measurements. For thin boundary layers, wake periodicity is observed. For slender pyramids (20° < ζ < 75°), periodic shedding of vortices is observed. The shedding frequency scales with the frontal (projected) width. For broad pyramids, wake periodicity cannot be related to vortex shedding. Vortex shedding appears related to the existence of a double vortex-structure along the side faces of the slender pyramids. For thick boundary layers, no wake periodicity is observed and the mean flow structure resembles that of broad pyramids. In all cases, the separation and reattachment point upstream and downstream of the obstacle scales with the projected frontal area.

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