Paper No. 18
D. R. Smith/J. C. Wachel, Rotordynamic Instability Problems in High Performance Turbomachinery — 1984, Texas A&M University, May 1984 .
When a compressor rotor experiences subsynchronous vibration, the problem is generally considered to be a shaft instability problem associated with the stability of the rotor on the bearing oil film. However, many times the high subsynchronous vibrations are forced vibrations caused by flow instabilities, such as stage stall. In these cases, modifications to improve the rotor stability by changing the bearings or seals will have little effect on the subsynchronous vibrations. It is therefore important to understand the differences between forced vibrations and self-excited vibrations so the problem can be properly diagnosed and corrected (References 1-4). The following is a list of characteristics of the two types of subsynchronous vibration.