Effects of Reynolds Number and Corner Radius on Two-Dimensional Flow Around Octagonal, Dodecagonal, and Hexdecagonal Cylinders HR-162, 1976

(1976) Effects of Reynolds Number and Corner Radius on Two-Dimensional Flow Around Octagonal, Dodecagonal, and Hexdecagonal Cylinders HR-162, 1976. Transportation, Department of

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Abstract

The effects of Reynolds number and corner radius on twodimensional flow around octagonal, dodecagonal and hexdecagonal cylinders were investigated. All models were studied at at least three model-relative wind orientations to determine the effect of angular alignment. In general it was found that the greatest drag coefficient was experienced with one of the corners pointing directly into the relative wind. The corner radii studied for each family of cylinders were 0.0, 9.1, 17.5, 24.5, 40.5, 57.7 and 74.2 percent of the radius of the inscribed circular cylinder. Data from these radii were compared with base line data obtained from a circular cylinder. It was found that at corner radii greater than 26 percent the hexdecagonal cylinder experiences a smaller drag than that of the circular cylinder. At corner radii smaller than 26 percent the drag of the hexdecagonal cylinder increases approximately linearly from a drag equal to that of a circular cylinder, to a value approximately 1.5 times that of a circular cylinder for the 0.0 percent corner radius. The dodecagonal cylinders experience the same trend, decreasing lineraly from a drag coefficient approximately 1.5 times that of a circular cylinder at a corner radius of 9.1 percent to a value of drag coefficient 3 percent greater than that of a circular cylinder at a corner radius of 34 percent. At corner radii greater than 0.34 the drag remains constant at this value. Drag coefficients for the octagonal cylinder are significantly greater than those of the circular cylinder except at corner radii approaching 100 percent. The effect of corner raidus on the coefficient of lift was negligible except at the larger corner radii where for increasing radius the lift coefficient approached zero. Model orientation and number of sides had the major effects on lift coefficient. As the number of sides increased the maximum values of lift decreased from 0.4 for 8-sided cylinders to approximately 0 for the 16-sided bodies. The direction of the force is determined by the angular orientation between the model and the relative wind. At orientations close to that having a flat side perpendicular to the relative wind the lift acts toward the side rotated in the downwind direction, while at orientations close to that having a corner pointing directly into the relative wind the lift force acts toward the side rotated up stream. At orientations where the upper and lower surfaces are symmetrical with respect to the relative wind the lift is approximately zero, but for rotations where this symmetry is missing the lift can be as large as 50 percent of the drag. Empirical equations are proposed for the prediction of the variation of the total aerodynamic force coefficient with change in model corner radius for a Reynolds number of 1,000,000.