Damping Oscillations of a Cylinder with a Coaxial Disk and a Stabilizer

Damped rotational oscillations of a cylinder equipped with a coaxial disk in the head part and a stabilizer in the tail part are studied. The elongation of the cylinder (the ratio of its length to diameter) is nine. The cylinder is mounted in the test section of the low-velocity wind tunnel with a wire suspension containing steel springs. In the equilibrium position, the cylinder axis is horizontal and parallel to the velocity vector of the incoming flow. A semiconductor strain gauge is attached to one of the suspension springs, which measures the time dependence of spring tension during oscillations. The output voltage of the strain gauge is sent to a PC oscilloscope, the digital signal of which is transmitted to the computer. After calibration of the device, the frequency and amplitude of damped rotational oscillations around the horizontal axis passing through the center of the cylinder and perpendicular to the velocity vector of the incoming flow were determined. The air flow enhances the rate of the damping of rotational oscillations of the cylinder. The air flow effect is described by analogues of rotational derivatives, which, in the case of bluff bodies, depend on the amplitude of the oscillations of the inclination angle of the body and on the amplitude of the angular velocity. A simple model of the effect of a stabilizer on rotational derivatives is proposed.