Effect of Parallel Plane Walls on Vortex-Induced Oscillations of a Cylinder

This paper addresses the vortex-induced oscillations of a spring-supported cylinder in a narrow channel. The characteristics of the two-dimensional laminar fluid flow in a narrow channel deeply depend on the oscillations of the cylinder. The main purpose of this paper is to clarify the effects of channel walls on the nonlinear interaction between transverse oscillations of the cylinder and the unsteady fluid flow in a narrow channel. The following two problems were investigated in order to estimate the effect of channel walls. First, the spring stiffness, which supports a cylinder in a narrow channel, is varied. As the spring stiffness becomes weak, the time history of the cylinder displacement includes not only an oscillating component (A.C.), but also a constant component (D.C.). The numerical results indicated that the D.C. component is generated by viscous force. Second, the frequency and amplitude of the cylinder oscillation and vortex-shedding frequency are measured in and around the lock-in region in case of a blockage ratio w = 2.5. The blockage ratio is the ratio of the channel width to the cylinder diameter. The results in the lock-in region in a narrow channel are different than in the general wall-less lock-in region where such behaviors have never been observed. In this study, the experiments are also performed at Reynolds numbers Re below 200. The cylinder motion and the fluid velocity are simultaneously measured with an angular displacement meter and a PIV (Particle Image Velocimetry) system, respectively. Furthermore, the experimental results are compared with the theoretical results that are obtained from the numerical calculation of the two-dimensional incompressible Navier-Stokes equations.