Damping oscillations of a cylinder with a coaxial disc and a stabilizer

Abstract

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

Keywords:

wind tunnel, rotational vibrations, strain gauge, cylinder