Effects of crossflow pulsation intensity on wake properties of a circular cylinder

The effects of the crossflow pulsation intensity on the wake flow properties of a circular-cylinder were experi-mentally studied in a wind tunnel. A rotating plate actuator technique was used to generate periodic crossflow oscillations. The Reynolds number and oscillation Strouhal number of the crossflow were fixed at 3111 and 0.074, respectively. The crossflow pulsation intensities were varied within the range between 0.035 and 0.074. The wake evolution processes were captured by laser-light-sheet-assisted smoke flow visualization method. The wake instability frequencies and instantaneous oscillating turbulent velocities were detected by a one-component hot-wire anemometer along with a high-speed data acquisition system. The triple-decomposition technique was applied to the instantaneous velocities to consider the effects of the crossflow oscillations on turbulence. The statistical turbulence flow properties such as the Lagrangian integral time and length scales were estimated. The time-averaged flow structures and vorticity contours in the wake were obtained to analyze the wake geometric parameters by averaging instantaneously captured PIV images. The results revealed that at a fixed Reynolds number, the wake instability frequency of a circular cylinder in oscillating crossflow would present a value in-between of the natural wake instability frequency and the crossflow oscillating frequency. The turbulence in-tensity and Lagrangian integral time and length scales in the cylinder wake of the oscillating crossflow were drastically larger than those in the natural crossflow. The time-averaged geometric parameters of the recircu-lation bubble in the circular-cylinder wake in oscillating crossflow were significantly smaller than those in the natural crossflow. The crossflow oscillations induced large scale flow motions and hence enhanced entrainment and mixing in the wake. These mechanisms expedited turbulent diffusion of momentum in the wake, and therefore the turbulence intensity and turbulence time and length scales were enlarged and the geometric pa-rameters of recirculation bubble were shortened when compared with those in the natural crossflow.