Experimental investigation on the influence of wind direction on the aerodynamic loads acting on low aspect-ratio prisms

Abstract

The results are described of measurements of the mean and fluctuating forces acting on low aspect-ratio triangular prisms placed vertically on a plane, having isosceles triangular crosssection with 60° or 90° apex angles and aspect ratios ranging from 1:0 to 3:0. The tests are carried out in a wind-tunnel by varying the wind direction between 0° and 180°, at a Reynolds number Re = 1:2 x 10^5. Furthermore, for the model with apex angle of 60° and aspect ratio 3:0, flow visualizations with tufts and hot-wire measurements are performed, which permit to characterize the wake morphology as a function of wind direction and to assess that an alternate vortex shedding always exists, with a frequency that is roughly inversely proportional to the wake width. The force measurements show that large variations in the mean values of the drag and cross-flow forces occurby varying µ, in strict connection with changes in wake flow features. The intensity of the fluctuating cross-flow forces, directly connected with vortex shedding, is found to vary significantly with flow orientation and aspect ratio, and to be approximately proportional to the streamwise projection of the body surface immersed in the separated wake. Finally, an increase in vortex shedding frequency is generally found with decreasing aspect ratio