Flow around a circular cylinder with axially arranged holes

In the present study, we experimentally investigated the flow around a circular cylinder with axially arranged holes (AAH). The wind-tunnel experiment was performed at Re = 3.2 ?? 10 while varying the angle of attack (??) from 0?? to 90??. At low ??, the passive jet from the AAH pushes near wake to the downstream, increasing the wake formation length. On the other hand, at high ??, blowing and suction through AAH occurs alternatively, rather decreasing the wake formation length. The passive jet generated by AAH can effectively control not only the wake where AAH is located, but also the wake between holes. As a result, the AAH reduce the drag on the cylinder up to 23.8% at low ?? but rather increase the drag at high ??, as compared to that on a smooth cylinder