Effect of shrink fits on threshold speeds of rotordynamic instability

Abstract

An investigation of the effect of shrink fits on threshold speeds of rotordynamic instability has been performed. It is known that running rotors at supercritical speed can result in some rotordynamic problems (asynchronous whirling). One such problem is the whirl instability caused by internal friction in a built-up rotor. Unlike passing through a resonance, where the amplitude of vibration increases and then decreases, the vibration of an unstable system continually grows exponentially; experimentally the vibration becomes very large but bounded. This can transfer large amounts of energy to the rotor system and can cause bearing damage or failure. Therefore, it is very important to understand the mechanism and the causes of violent rotor oscillation due to internal damping and to include it in rotordynamic models to assess the stability of the system. The free-free rap tests were conducted at different interference fits. The free vibration responses were analyzed, in order to identify the nature of the damping in the system and quantify it. Running tests were conducted to determine the onset speed of instability experimentally. Finally, the onset speed of instability was predicted analytically using the model presented by Gunter and the rotordynamic computer code (XLTRC) and compared with the experimental values.