Backward whirl investigations in isotropic and anisotropic systems with gyroscopic effects

In the dynamics of rotors, the Campbell diagram is a very powerful tool for presenting the natural frequencies and finding critical speeds of rotating machinery. However, a conventional Campbell diagram can not explain exactly why there is no backward critical speed in isotropic systems but there is in anisotropic systems. This paper reviews the existing methodologies used to solve the eigenvalue problem and discusses the advantages and limitations that they have in describing the rotordynamics behaviour. It also attempts to provide a relation between the strength of the mode and the degree of anisotropy, using a combination of real and complex modal analysis.