On the Flutter and Drag Forces on Flexible Rectangular Canopies in Normal Flow

Abstract

The paper presents results of experimental investigations on flexible rectangular canopies fixed at two edges (tapes). Data are presented for the aerodynamic drag as a function of the planform area, the slenderness, and the Reynolds number. The slenderness varies from 3.3 to 30. The Reynolds number is limited to 2×106. The wind speed is in the range 6–19m∕s. The results show that the drag decreases with the increasing aspect ratio. The dominant parameter is the slenderness; a second dominant factor is the planform area. The drag is only weakly dependent on the Reynolds number. The analysis of the drag data indicates that a proper scaling parameter is the crosswise length scale. When normalization is done, the data tend to collapse into a single curve. A further study addressed the drag characteristics of the canopies with perforated planforms. Perforation of up to 6% of the planform area has been considered. Corrections for air permeability of the fabric are introduced. The drag is reduced roughly linearly with perforated area. A detailed study into the flutter characteristics of the canopies in the turbulent wind is presented. The investigation has highlighted different modes of oscillations, including deformations through folding and twisting, vertical flapping, rotations, and cross-type oscillations.