Flow over a circular cylinder with a flexible splitter plate

In the present work, we study the flow field around, and forces acting on, a circular cylinder with an attached flexible splitter plate/flap. Two cases of flap length (L/D), namely, L/D=5andL/D=2 have been investigated focusing on the effect of variations in flap flexural rigidity, EI. We find that for a range of EI and Reynolds numbers Re=UD/nu,a non-dimensional bending stiffness K-& lowast;=EI/((1/2)rho(UL3)-L-2)collapses flap motion and forces on the system well, as long as Re>5000. In the L/D=5 flap case, two periodic flap deformation regimes in the form of travelling waves are identified (modes IandII), with mode I occurring at K-& lowast;approximate to 1.5x10(-3)and mode II at lower K-& lowast; values (K-& lowast;<3x10(-5)). In the L/D=2 flap case, we find a richer set of flapping modes (modes A, B,C and D) that are differentiated by their flapping characteristics (symmetric/asymmetric and amplitude). Force measurements show that the largest drag reduction occurs in modeI (L/D=5) and mode C (L/D=2), which also correspond to the lowest lift and wake fluctuations, with the mode C wake fluctuations being lower than even the rigid splitter plate case. In contrast, the highest fluctuating lift, in both L/D cases, occurs at higher K-& lowast;, when the wake frequency is close to the first structural bending mode frequency of the flap. The observed rich range of flap/splitter plate dynamics could be useful for applications such as drag reduction, vibration suppression, reduction of wake fluctuations and energy harvesting.