Techno Press
Techno Press

Wind and Structures   Volume 26, Number 5, May 2018, pages 293-304
Flow structures around rectangular cylinder in the vicinity of a wall
J.F. Derakhshandeh and Md. Mahbub Alam

Abstract     [Full Text]
    A numerical study is conducted on the flow characteristics of a rectangular cylinder (chord-to-width ratio C/W = 2 - 10) mounted close to a rigid wall at gap-to-width ratios G/W = 0.25 - 6.25. The effects of G/W and C/W on the Strouhal number, vortex structure, and time-mean drag and lift forces are examined. The results reveal that both G/W and C/W have strong influences on vortex structure, which significantly affects the forces on the cylinder. An increase in G/W leads to four different flow regimes, namely no vortex street flow (G/W < 0.75), single-row vortex street flow (0.75< G/W < 1.25), inverted two-row vortex street flow (1.25 < G/W < 2.5), and two-row vortex street flow (G/W > 2.5). Both Strouhal number and time-mean drag are more sensitive to C/W than to G/W. For a given G/W, Strouhal number grows with C/W while time-mean drag decays with C/W, the growth and decay being large between C/W = 2 and 4. The time-mean drag is largest in the single-row vortex street regime, contributed by a large pressure on the front surface, regardless of C/W. A higher C/W, in general, leads to a higher time-mean lift. The maximum time-mean lift occurs for C/W = 10 at G/W = 0.75, while the minimum time-mean lift appears for C/W = 2 at the same G/W. The impact of C/W on the time-mean lift is more substantial in single-row vortex regime. The effect of G/W on the time-mean lift is larger at a larger C/W.
Key Words
     boundary layers; rectangular cylinder; Strouhal number; vortex shedding frequency
J.F. Derakhshandeh: School of Mechanical Engineering of University of Adelaide, Australia
Md. Mahbub Alam: Institute for Turbulence-Noise-Vibration Interaction and Control, Shenzhen Graduate School,
Harbin Institute of Technology, Shenzhen 518055, China

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