Publication Date:
2016-12-22
Description:
The wake of polygonal cylinders with side number N = 2 ∼ ∞ is systematically studied based on fluid force, hot-wire, particle image velocimetry and flow visualisation measurements. Each cylinder is examined for two orientations, with a flat surface or a corner leading and facing normally to the free stream. The Reynolds number Re is 1:0 × 104 × 1:0 × 105, based on the longitudinally projected cylinder width. The time-averaged drag coefficient CD and fluctuating lift coefficient on these cylinders are documented, along with the characteristic properties including the Strouhal number St, flow separation point and angle θs, wake width and critical Reynolds number Rec at which the transition from laminar to turbulent flow occurs. It is found that once N exceeds 12, Rec depends on the difference between the inner diameter (tangent to the faces) and the outer diameter (connecting corners) of a polygon, the relationship being approximately given by the dependence of Rec on the height of the roughness elements for a circular cylinder. It is further found that CD versus ξ or St versus ξ for all the tested cases collapse onto a single curve, where the angle ξ is the corrected θs associated with the laterally widest point of the polygon and the separation point. Finally, the empirical correlation between CD and St is discussed. © 2016 Cambridge University Press.
Print ISSN:
0022-1120
Electronic ISSN:
1469-7645
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
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