Square-cylinder flow patterns modulated using an upstream control rod

This investigation examines the flow patterns, vortex-shedding frequency and aerodynamic performance of a combination of an upstream control rod and a square cylinder. The flow behaviors were tested using various Reynolds numbers, rotation angles and spacing ratios. The smoke-wire scheme was utilized to visualize the flow structures. Particle image velocimetry (PIV) was applied to analyze the global velocity fields and streamline patterns. A hot-wire anemometer was used to probe the vortex-shedding frequency behind the control rod and the square cylinder. Moreover, a linear pressure scanner was employed to measure the surface pressure on the square cylinder. Accordingly, the aerodynamic parameters were determined using the surface-pressure profiles. Three characteristic flow modes - single, attached and bi-vortex-street - were categorized by varying the Reynolds number and space ratio. In the attached mode, the upstream control rod dominated the flow behaviors. Furthermore, in the attached mode, the experimental data indicate that the drag was 57% lower than that without the upstream control rod.