Effect of rotation axis position of the cylinder on its rotational oscillations in the air stream

Abstract

Steady rotational oscillations of circular cylinder in the air stream are studied experimentally. Cylinders are fixed by an elastic spring suspension, which allows making rotational oscillations about an axis perpendicular to the velocity vector of the incoming flow. Semiconductor strain gauge S-50 attached to the PC-oscilloscope Velleman PCS500A measures the dependence of the tension of one of the suspension springs on time. The results of the tension spring measurement are used to determine the amplitude of steady rotational oscillations of the cylinder in the flow. On the basis of experimental data obtained for different air flow velocities, the parameters of the mathematical model describing the oscillations of the cylinder in the flow are determined. Tests were conducted for cylinders with elongations 1.5, 2 and 3 at several positions of the axis of rotation. For the cylinder with elongation 2 maximum amplitude of oscillation occurs when the rotation axis passes through the geometric center of the cylinder. The amplitude of the oscillations of the cylinder with elongation 1.5 exceeds the amplitude of the oscillations of the cylinder with elongation 2, if the distance from the axis of rotation to downwind end is equal to the diameter of the cylinder. But in this configuration oscillations do not develop from the state of rest. In all experiments the equilibrium inclination angle of the cylinder axis with respect to the velocity vector of the the incoming flow varied in the range of several degrees. The mathematical model correctly describes the influence of angle of inclination on the amplitude of oscillation. Refs 14. Figs 6.