The effects of free-stream turbulence and angle of attack on the aerodynamics of a cylinder with rectangular 5:1 cross section

The aerodynamics of a stationary two-dimensional cylinder with rectangular 5:1 cross section is the object of an international experimental and numerical benchmark study (BARC). The unsteady flow past such a bluff body is governed by the impinging shear-layer instability mechanism, which is also responsible for potential flow-induced vibrations. This paper discusses the characteristics of the high-Reynolds-number unsteady flow over the cylinder, investigated in the wind tunnel through pressure and force measurements on a sectional model in smooth and turbulent flows. In addition, hot-wire anemometry measurements of the velocity in the wake of the cylinder were carried out in smooth flow. The study is particularly focused on understanding the influence of free-stream turbulence and angle of attack on the aerodynamic behavior of the body. Key features are highlighted, such as a slight Reynolds-number dependence of force coefficients and Strouhal number in smooth flow, or the turbulence-induced variation of the length of the separation bubbles along the lateral sides of the cylinder. Incoming turbulence is also found to affect the vortex-shedding mechanism of impinging shear-layer instability, promoting the switch from a dominant mode to another. Finally, the wake measurements described some vortex-shedding features, confirming a slight Reynolds-number dependence of the Strouhal frequency.