Scaling of the time-mean characteristics in the polygonal cylinder near-wake

Abstract

The near wake of the polygonal cylinder with the side number N = 3 ~ ∞ is systematically studied based on particle image velocimetry (PIV) and load-cell measurements. Each cylinder is examined for two orientations, with either one leading side or leading corner. The Reynolds number Re = (1.0 ∼ 6.0) × 104 , defined by the longitudinally projected cylinder width. The dependence of the wake characteristic parameters on the cylinder orientation and N is discussed, and wake scaling analysis is conducted based on these parameters. It is found that the velocity deficit and half width of the wake scale well with the reverse flow zone length and recirculation bubble width, whilst the Strouhal number, drag and fluctuating lift coefficients scale well with the vortex formation length and wake width. The unveiled scaling relationships cast insight into the intrinsic physical connections between the aerodynamic forces and vortex formation and between the polygonal cylinder wakes of N = 3 ~ ∞, suggesting that the understanding of the time-mean wake behind individual polygonal cylinder can be unified to that of the circular cylinder wake.