Effect of the Rotation Axis Position of a Cylinder on Its Rotational Oscillations in an Air Flow

Steady-state rotational oscillations of circular cylinders in an air flow are experimentally studied. The cylinders are fixed on an elastic spring suspension allowing rotational oscillations around an axis perpendicular to the vector of incident flow velocity. A C-50 semiconductor strain gauge connected to a Velleman PCS500A PC-oscilloscope measures the tension of one of the suspension springs as a function of time. Spring tension measurements are used to determine the amplitude of steady-state rotational oscillations of the cylinder in the flow. Experimental data obtained at various airflow velocities were used to calculate the parameters of a mathematical model describing the cylinder oscillations in the flow. Tests were conducted for cylinders with aspect ratios of 1.5, 2, and 3 at several positions of the rotation axis. For a cylinder with an aspect ratio of 2, the maximum oscillation amplitude is observed when the rotation axis passes through the geometric center of the cylinder. The oscillation amplitude of a cylinder with an aspect ratio of 1.5 exceeds that of a cylinder with an aspect ratio of 2 if the distance from the axis of rotation to the leeward end is equal to the cylinder diameter. However, oscillations in this configuration do not develop from the state of rest. In all experiments, the equilibrium tilt angle of the cylinder axis varied within a few degrees relative to the incident flow velocity vector. The mathematical model correctly describes the effect of tilt angle on the oscillation amplitude.