Numerical study of flow control via the interaction between a circular cylinder and a flexible plate

Flow control through the interaction between a fixed circular cylinder and a detached flexible plate is numerically investigated in this study. Based on the diameter of the cylinder (d), the laminar flow with a Reynolds number of 100 is considered in this work. A flexible plate undergoing fish-like motion is placed in either the downstream or upstream of the cylinder. The gap between the cylinder and the plate (S), the oscillation frequency (Stf) and the oscillation amplitude (A) are crucial parameters. When the flexible plate is in the downstream of the cylinder, a stable flow pattern is generated under some conditions (for example, Stf=0.4 together with A/d=0.1 at S/d=0.1-2.5 and Stf=0.2 with A/d=0.2-0.4 at S/d=1). Meanwhile, compared to the case of the rigid plate, a further drag reduction is obtained due to the motion of the flexible plate (the maximum drag reduction is 2.9% at A/d=0.2, Stf=0.2 and S/d=1). In addition, the net saving can also be found, which means that both drag reduction and energy saving can be achieved (the maximum net saving is 98.54% at A/d=0.5, Stf=0.1 and S/d=2.5). In contrast, when the flexible plate is in the upstream of the cylinder, a much smaller drag can be achieved compared to the case of the flexible plate in the downstream. Moreover, a significant drag reduction can be attained compared to the rigid plate case (the maximum drag reduction is approximately 28% at A/d=0.5, Stf=0.5 and S/d=2). The established results in this study imply that the flexibility of the plate is of importance in controlling the flow over a bluff body.