Galloping and Flutter

Abstract

In this chapter we will consider flow-induced oscillations of structures with non-circular cross sections. For these structures, their orientation with respect to the incoming flow influences the mean flow forces that act on the structure, and as opposed to a structure with a circular cross-section, the mean flow force in the direction perpendicular to the flow direction (i.e., the mean lift force) is not necessarily zero. Therefore, the mean flow forces could cause oscillations, if the structure is flexible or flexibly mounted. In these cases, although vortex shedding can be observed, they are due to the fact that a bluff body is placed in flow, and they are not the cause of oscillations. Besides a bluff body with non-circular cross-section, a streamlined body placed in flow can experience nonzero mean lift. The most well-known example of a streamlined body in flow with nonzero mean lift force is an asymmetric airfoil, or any airfoil (symmetric or asymmetric) placed at an angle with respect to the incoming flow. In this chapter we will see how these nonzero mean values of lift and drag can cause oscillations in flexibly mounted structures. These oscillations can be galloping or flutter.