Influence of surface suction on wake characteristics behind a circular cylinder

The influence of surface suction on wake characteristics behind a circular cylinder was experimentally studied. Hydrogen bubble flow visualization technique and particle image velocimetry (PIV) measurement for a circular cylinder wake were carried out in a water tunnel at different suction flow rates. The wake width is decreased with increasing suction flow rate based on the flow visualization results. The time-averaged flow field and instantaneous flow field captured by PIV were analyzed. The results show that the suction reduces the recirculation area, the peak area of Reynolds tress, turbulent kinetic energy, and flow blockage. Power spectrum density (PSD) analysis of instantaneous velocity field shows that the suction increases vortex shedding frequency near the cylinder. The proper orthogonal decomposition method was applied to the PIV data. The result indicates that the suction has a strongly suppressed effect on the first two modes. PSD analysis of a₁ and a₂ shows the first two modes’ characteristic frequency is equal to the major frequency. A circulation process of vortex formation and shedding is presented by the low-order flow field consisting of the time-averaged flow field and the first two modes at different suction flow rates. The low-order flow field consisting of the time-averaged flow field and mode 3 and mode 4 shows that the periodic large-scale symmetric shedding vortices are removed due to the suction.