Wind loading of a finite prism: aspect ratio, incidence and boundary layer thickness effects

摘要

A systematic set of low-speed wind tunnel experiments was performed at Re = 6.5 x 10(4) and 1.1 x 10(5) to study the mean wind loading experienced by surface-mounted finite-height square prisms for different aspect ratios, incidence angles, and boundary layer thicknesses. The aspect ratio of the prism was varied from AR = 1 to 11 in small increments and the incidence angle was changed from alpha = 0 degrees to 45 degrees in increments of 1 degrees. Two different boundary layer thicknesses were used: a thin boundary layer with 6ID = 0.8 and a thick boundary layer with delta/D = 2.0-2.2. The mean drag and lift coefficients were strong functions of AR, alpha, and delta/D, while the Strouhal number was mostly influenced by alpha. The critical incidence angle, at which the prism experiences minimum drag, maximum lift, and highest vortex shedding frequency, increased with AR, converged to a value of alpha(c) = 18 degrees +/- 2 degrees once AR was sufficiently high, and was relatively insensitive to changes in delta/D. A local maximum value of mean drag coefficient was identified for higher-AR prisms at low alpha. The overall behaviour of the force coefficients and Strouhal number with AR suggests the possibility of three flow regimes.