Freestream Turbulence Effects on Galloping

Galloping is the term used to describe large amplitude single degree-of-freedom motions of a structure associated with a sectional aerodynamic force characteristic which produces a force in the direction of and in phase with the cross-wind motion. Detailed experimental investigations show that freestream turbulence has profound effects on the galloping behavior of a square tower. It is generally believed that increase in freestream turbulence increases the turbulence mixing in the separated shear layers and the rate of entrainment from the wake, and decreases the radius of curvature of the shear layers. These effects significantly alter the transverse force characteristic and thus the galloping behavior of the tower. It is also shown that the fine-scale turbulence produced by a thin rod upstream of the stagnation streamline of the tower is sufficient to cause these effects.