Experimental evaluation of the mean and fluctuating forces on triangular prisms in cross-flow

The results are described of the measurement of the mean and fluctuating forces acting on triangular prisms placed vertically on a plane, having isosceles triangular cross-section with 60° or 90° apex angles and aspect ratio ranging from 1.0 to 3.0. The tests are carried out in a wind-tunnel by varying the wind direction theta between 0° and 180°, at a Reynolds number Re ≈ 1.2 x 105. Furthermore, for the model with apex angle of 60° and aspect ratio 3.0, hot-wire measurements and flow visualizations with tufts are performed, in order to characterize the wake morphology and to determine the vortex shedding frequency as a function of the wind direction. The results show that large variations in the mean values of the drag and cross-flow forces occur by varying theta. Moreover, the fluctuations of the cross-flow force, connected with vortex shedding, are found to vary significantly with flow orientation, both in terms of frequency and intensity; in particular, the latter is a function of the streamwise projection of the body surface immersed in the separated wake. Moreover, an increasing vortex shedding frequency is generally found with decreasing aspect ratio