The effect of end conditions on rotational vortex-induced vibrations

In this paper, we experimentally study the translational and recently discovered rotational vortex-induced vibrations (VIVs) of a finite-span circular cylinder mounted on an elastic beam in a wind tunnel for Reynolds numbers (1−9.3)×103. The objective of this research is to investigate the vortex shedding structure along the cylinder's span, and how it changes under different end conditions. The vibration amplitudes, vortex shedding frequencies, and phases of the vortices shed from the cylinder were measured. We examine the influence of four types of end conditions (a free end, a hemisphere, and attached and unattached end plates) on the excitation of translational and rotational VIV as well as on the wake behind the cylinder in the rotational lock-in mode. The use of an end condition different from the free end found to result in a shift of both lock-in ranges to smaller velocities. The type of end condition strongly influences the average phase of vortex shedding, and the shape of its dependence along the cylinder remains quite far from the case of two-dimensional vortex shedding even for end plates. The phase difference in symmetrical modes relative to the axis of rotation in the case of rotational vibrations is approximately equal to π, and for transversal vibrations, it is almost zero. For rotational oscillations, the phase change near the rotational axis occurs abruptly, which is associated with the presence of a supporting beam, which plays the role of a spitter plate.