Effect of Turbulence on Galloping Instability

The nonlinear quasi-steady theory of galloping oscillations is extended to incorporate the variations of the mean angle of attack with wind speed due to drag as is the case with transmission lines and suspension bridges. This effect can turn a section having a stable equilibrium position, such as the D-section, into an unstable one and change the familiar patter of galloping. The oscillations grow with wind speed only up to a point and then cease. The effect of turbulence was experimentally investigated with a D-section, rectangular sections 2/3 and 3/2, and the cruciform section. It was found that turbulence considerably increases the tendency to galloping instability of the D-section and of the 2/3 rectangular section. The observations indicate that the galloping oscillations of ice covered conductors can be strongly encouraged by the effects of turbulence and the variations of the mean angle of attack due to drag.