Modulation of wake flow and aerodynamic behaviors around a square cylinder using an upstream control bar

This investigation studies the flow patterns, vortex-shedding frequency, turbulence intensity (T.I.), drag coefficient (CD) and lift coefficient (CL) around a square cylinder using an upstream control bar. The flow behaviors were investigated using various Reynolds numbers (Re), rotation angles (θ) and spacing ratios (L/w). The surface oil-flow visualization was utilized to observe the flow structures. The surface oil-flow patterns were classified into three characteristic flow modes - twin-bubble, leading-edge bubble, and uninfluenced - using various Re and L/w at θ = 0°. Four characteristic flow modes - uninfluenced, twin-bubble, leading-edge bubble, and attached flow - were defined by changing L/w and θ while Re = 6 × 104. Hot-wire anemometry was used to measure the vortex-shedding frequency behind the square cylinder. With the influence of upstream control bar, the highest Strouhal number of 0.225 and the lowest T.I. of 10.4% occurs in the leading-edge bubble mode at θ = 0°. Additionally, the linear pressure scanner was utilized to detect the surface pressure on the square cylinder, and the aerodynamic parameters were determined from the surface-pressure profiles. In the leading-edge bubble mode, CD has the lowest and CL has the highest value at θ = 0°.