Wind and Structures

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

  • Heng, Herman (Department of Mechanical Engineering, University of Saskatchewan) ;
  • Sumner, David (Department of Mechanical Engineering, University of Saskatchewan)
  • Received : 2019.09.05
  • Accepted : 2020.03.09
  • Published : 2020.09.25
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Abstract

A systematic set of low-speed wind tunnel experiments was performed at Re = 6.5×104 and 1.1×105 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 α = 0° to 45° in increments of 1°. Two different boundary layer thicknesses were used: a thin boundary layer with δ/D = 0.8 and a thick boundary layer with δ/D = 2.0-2.2. The mean drag and lift coefficients were strong functions of AR, α, and δ/D, while the Strouhal number was mostly influenced by α. 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 αc = 18° ± 2° once AR was sufficiently high, and was relatively insensitive to changes in δ/D. A local maximum value of mean drag coefficient was identified for higher-AR prisms at low α. The overall behaviour of the force coefficients and Strouhal number with AR suggests the possibility of three flow regimes.

Keywords

Acknowledgement

Financial support from the NSERC Discovery Grants program (Grant No. 2018-03760), the College of Engineering's Graduate Research Fellowship program, and the Department of Mechanical Engineering's Graduate Scholarships program, is gratefully acknowledged. The technical assistance of Shawn Reinink, Rob Peace, and Engineering Shops is also recognized.

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