Scaling of the Wall Pressure Field Around Surface-Mounted Pyramids and Other Bluff Bodies

Abstract

The turbulent flow around square-based, surface-mounted pyramids, of height h, in thin and thick boundary layers was experimentally investigated. The influence of apex angle ζ and angle of attack α was ascertained from mean surface flow patterns and ground plane pressure measurements taken at a Reynolds number of 3.3×104 based on h. For both boundary layer flows, it was found that the normalized ground plane pressure distributions in the wakes of all the pyramids for all angles of attack may be scaled using an attachment length (Xa′) measured from the upstream origin of the separated shear layer to the near-wake attachment point on the ground plane. It was also shown that this scaling is applicable to data reported in the literature for other bluff body shapes, namely, cubes, cones, and hemispheres. The ground plane pressure coefficient distributions in the upstream separated flow region, for all the shapes and angles of attack examined, were found to collapse onto two curves by scaling their streamwise location using a length scale (Xu), which is a function of the frontal projected width of the body (w′) and the height of the body. These two curves were for cases where δ∕h<1 (“thin” boundary layer) or δ∕h≥1 (“thick” boundary layer), where δ is the oncoming boundary layer thickness. Further work is required to provide a more detailed statement on the influence of boundary layer thickness (or state) on the upstream pressure field scaling.