The dynamical behaviour of cylindrical structures in axial flow

This is a review on the effect of axial flow on cylindrical structures. It is shown that axial flow may cause fluidelastic instabilities at sufficiently high flow velocities. However, for the range of flow velocities and other parameters pertaining to most industrial systems, the effect of purely axial, uniform steady flow is to damp free motions. Nevertheless, departures from such ideal flow conditions induce small amplitude vibration, termed sub-critical vibration. The underlying mechanism of this vibration is examined and the various means available for predicting its amplitude are discussed. These latter are either empirical or analytical (generally semi-empirical); the analytical methods are further classified into three categories accordingly as they postulate the vibration to be forced, parametric or self-excited. The measure of success achieved in predicting sub-critical vibration amplitude is discussed, and possible reasons for its being generally poor. At present, the amplitude may be predicted typically to within one order of magnitude.