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Research Papers: Fundamental Issues and Canonical Flows

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

[+] Author and Article Information
Antonio Filippone

School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, George Begg Building, P.O. Box 88, Manchester M60 1QD, UKa.filippone@manchester.ac.uk

J. Fluids Eng 130(6), 061203 (May 19, 2008) (8 pages) doi:10.1115/1.2928431 History: Received December 06, 2006; Revised August 20, 2007; Published May 19, 2008

## 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.

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## Figures

Figure 2

Experimental arrangement

Figure 3

Support drag for force calibration

Figure 4

Rigid rotation, up and down movement

Figure 5

Alternate flutter mode

Figure 6

Folding of slender tape

Figure 7

Canopy deformation by twisting

Figure 8

Summary of flutter modes as a function of slenderness and planform area

Figure 9

CD based on planform area for all tapes

Figure 10

Drag coefficient based on Ae=D∕qb

Figure 11

Effects of slenderness at fixed planform area

Figure 12

CD for tapes of slenderness l∕b=10, and comparison with semiempirical formula for normal flat plates

Figure 13

Perforated tape in the wind tunnel, A=0.050m2, l∕b=10, Ap∕A=0.06, and U=11.0m∕s

Figure 14

Effects of perforated area on drag

Figure 15

Effects of perforated tapes on drag coefficient (corrected)

Figure 16

Drag/weight for selected tapes

Figure 1

Example of tape, stable in the wind

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