Two-dimensional study of a rectangular bluff body with a forebody airtight screen at a relatively small distance

The aerodynamics of a two-dimensional system, composed by a rectangular cylinder and a solid screen close to the windward face, is studied by performing smooth-flow experimental tests and numerical simulations. The aim of the study is to understand if and how a relatively thin screen, placed at a distance an order of magnitude smaller than the cross-section dimensions, affects the aerodynamic behavior of the system. The results highlight the key role played by the oscillating flow occurring, for a wind nearly perpendicular to the screen, in the cavity behind it, which connects opposite sides of the body. Such a secondary flow is able to alter significantly the fluid motion past the cylinder. The effects of several parameters of the system have been investigated, such as the screen distance and the baseline prism geometry. The pressure measurements and the numerical flow visualizations highlighted the significantly different flow features induced by the presence of the screen, which is even able in certain conditions to promote the mean reattachment of the shear layers separating from the front corners of the cylinder. In contrast, global aerodynamic quantities clearly reveal the effect of the screen only for a non-null angle of attack. Furthermore, an approximate method is proposed to estimate the regime of the oscillating flow in the cavity, which is deemed crucial for a correct design of wind tunnel tests able to reproduce the actual full-scale behavior.