Abstract
In this article case studies are presented involving rotordynamic instability of modern high-speed turbomachinery relating the field data to analytical methods. The studies include oil seal related field problems, instability caused by aerodynamic cross-coupling in high-pressure, high-speed compressors, and hydrodynamic bearing instability resulting in subsynchronous vibration of a high-speed turbocharger. It has been shown that the analytical tools not only help in problem diagnostics, but also aid in problem resolution. Examples are presented showing how analytical methods, when appropriately applied, can solve rotordynamic instability and result in stable rotor system.