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# Drag Reduction Due to Cut-Corners at the Front-Edge of a Rectangular Cylinder With the Length-to-Breadth Ratio Being Less Than or Equal to Unity

[+] Author and Article Information
Mitsuo Kurata

Department of Mechanical Engineering, College of Engineering, Setsunan University, 17-8 Ikedanaka-Machi, Neyagawa, Osaka 572-8508, Japan

Yoshiaki Ueda

Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, Nishi 8, Kita 13, Kita-Ku, Sapporo, Hokkaido 060-8628, Japany-ueda@eng.hokudai.ac.jp

Teruhiko Kida

Division of Mechanical Engineering, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-Cho, Sakai, Osaka 599-8531, Japan

Manabu Iguchi

Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, Nishi 8, Kita 13, Kita-Ku, Sapporo, Hokkaido 060-8628, Japan

J. Fluids Eng 131(6), 064501 (May 13, 2009) (5 pages) doi:10.1115/1.3129123 History: Received February 20, 2008; Revised March 11, 2009; Published May 13, 2009

## Abstract

The flow past a rectangular cylinder with small cut-corners at the front-edge is investigated to discuss a relation between drag reduction and the cutout dimension. The rectangular shape is selected in eleven kinds of the length-to-breadth ratio from 2/6 to 6/6 (square prism) with the small rectangular-shaped cut-corners at the front-edge. The wind tunnel experiment is carried out to obtain time-averaged hydrodynamic forces measured by the force transducer at $Re≈50,000$. The contour map of the hydrodynamic coefficients with respect to the cutout dimension are shown to investigate the relation between the drag reduction and the cutout shape. In the contour map for the zero angle of attack, the region of the effective drag reduction achieved, in which the value of the drag coefficient is less than that of a circular cylinder at the same Reynolds number, is observed to become wide with the increase in the length-to-breadth ratio and it is independent of the angle of attack, $α$, within $α$ being small. Furthermore, it is shown that there is a condition in which the drag reduction of $CD⪅1.5$ can be achieved even when the Strouhal number is less than 0.2.

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## Figures

Figure 8

Strouhal number, St, versus drag coefficient, CD, for various values of the length-to-breadth ratio, b/a

Figure 7

Contour map of CD with respect to the angle of attack of α degree and c2/a in the case of c1/a=0.10. (Left) b/a=2/6, (center) b/a=4/6, and (right) b/a=6/6

Figure 6

Hydrodynamic coefficients against the angle of attack of α degree in the case of c1/a=0.10 and c2/a=0.15. (Left) b/a=2/6, (center) b/a=4/6, and (right) b/a=6/6

Figure 5

Drag and lift coefficients, CD and CL, of a rectangular cylinder with cut-corners of c1=0.10 and c2=0.15 against the angle of attack of α degree. (Circle) b/a=2/6, (triangle) b/a=4/6, and (square) b/a=6/6.

Figure 4

Contour map of (top) CD and (bottom) CPb with respect to cutout dimension. (Left) b/a=2/6, (center) b/a=4/6, and (right) b/a=6/6

Figure 3

Hydrodynamic coefficients: (solid line) CD, (dashed line) CPb, and (dotted line) St versus c1/a for (left) b/a=2/6, for (center) b/a=4/6, and for (right) b/a=6/6. (Square) c2/a=0.0, (circle) c2/a=0.05, (triangle) c2/a=0.1, (plus) c2/a=0.15, (rhombus) c2/a=0.2, and (cross) c2/a=0.25

Figure 2

Length-to-breadth ratio, b/a, versus hydrodynamic coefficients: (solid line) CD, (dashed line) CPb, (dotted line) St for various cutout shapes, (circle) c1/a=c2/a=0.0; (square) c1/a=0.1 and c2/a=0.15, and (triangle) c1/a=0.1 and c2/a=0.2. The solid symbols are earlier comparative results for c1/a=c2/a=0.0 by (solid circle) Bearman and Trueman (8), (solid square) Igarashi (9), and (solid triangle) Nakaguchi (10).

Figure 1

Coordinate system and physical settings

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