Vortex Shedding Intermittency and Its Effects on the Aerodynamics Forces of a Finite-Length Square Cylinder

Abstract

The aerodynamic forces on a wall-mounted finite-length square cylinder are experimentally investigated. The width of the tested model d = 200 mm, and the aspect ratio H/d = 5. The oncoming flow velocity U ∞ = 13 m/s, corresponding to a Reynolds number of 1.73 × 105 based on U ∞ and d. It is found that the time-averaged drag coefficient \( \overline{{C_{D} }} \) and rms value of lift coefficient \( C^\prime_{L} \) of the finite-length cylinder are both smaller than those of 2D square cylinder. Two typical flow modes occur in the flow around the finite-length cylinder: Mode 1 is characterized by alternating spanwise vortex shedding, corresponding to a higher drag and large amplitude fluctuation of lift; Mode 2 is characterized by symmetrical vortex shedding, corresponding to a lower drag and the lift without periodic fluctuation. At the lower part of cylinder, \( C^\prime_{L} \) of Mode 1 is about one times larger than that of Mode 2, this difference reduces gradually with approaching to the free end. The spanwise correlation of aerodynamic force is stronger in Mode 1.