Mean wake and aerodynamic forces for surface-mounted finite-height square prisms of very small aspect ratio

Abstract

The mean flow field, aerodynamic forces, bending moment and Strouhal number (St) were investigated for isolated surface-mounted finite-height square prisms of very small aspect ratio (AR). The Reynolds number was Re [Formula: see text] for the velocity measurements and [Formula: see text] for the force, bending moment and St measurements. Prisms with AR = 0.5, 0.7 and 1 were considered, under two different boundary layer thicknesses of [Formula: see text]–0.8 (thin) and [Formula: see text] (thick). For both boundary layers, the mean drag force coefficient showed a sharper increase with AR compared with taller prisms, and the mean normal force coefficient increased smoothly, with a lower magnitude than pressure-based normal force coefficients. An approximately constant point of action of the drag force was found for AR < 1. While the thick boundary layer caused the spectral peaks to weaken and St to decrease, some periodicity was still found for all AR. These features were connected to the changes in the mean wake of the prisms with AR and [Formula: see text]. A smaller AR and larger [Formula: see text] had similar effects, causing the wake to shorten, the probability and type of reattachment of the flow on the free end to change, and the mean wake structure to transition from a streamwise wake vorticity pattern to an inner vorticity pattern. The prism with AR = 1 showed a dipole wake structure similar to that of taller prisms, while the unique wake topology of prisms with AR < 1 was found to be responsible for the different force and St trends identified in this range of AR.