Effects of oncoming flow conditions on the aerodynamic forces on a cantilevered square cylinder

The aerodynamic forces on a cantilevered square cylinder with a height-to-width ratio (H/d) of 5 in a crossflow were experimentally investigated in a closed-loop low-speed wind tunnel. The freestream oncoming flow velocity (U∞) ranged from 5 to 45 m/s, corresponding to Reynolds numbers, based on U∞ and d, of 0.68 × 105 to 6.12 × 105. Two different oncoming flow conditions were tested. In case 1, the majority of the cylinder span was in the uniform flow, except the lower 1d which was immersed in a thin turbulent boundary layer; in case 2, the tested cylinder was completely immersed in a turbulent boundary layer. In both cases, the Reynolds number had a negligible effect on the aerodynamic forces of the cylinder. The predominant vortex shedding frequency was constant along the cylinder span, regardless of the thickness and nature of the boundary layer. In case 1, the lift fluctuated periodically with a large amplitude or did not exhibit obvious periodicity, which correspond to the anti-symmetric and symmetric vortex shedding modes, respectively. Proper orthogonal decomposition (POD) analysis showed that, in case 2, anti-symmetric vortex shedding tends to occur, instead of the symmetric mode, thus resulting in a larger fluctuating lift than that observed case 1.