Oil whirl / whip
Oil whirl is a self-excited fluid disturbance that typically occurs in plain bearings. This can happen for a number of reasons, including:
- Misalignment – bearing not loaded.
- Excessive clearance
- Lightly loaded, low damping
The whirling of the oil creates a characteristic source of vibration in the range of approximately 0.38X to 0.48X
Oilwhipping is a very destructive condition. This condition can occur when the machine speed exceeds twice the critical speed (or the first resonance of the balancing rotor). Therefore, the critical speed is close to the oil swirl frequency. The oil vortex will resonate and create a violent state. The vibration level is very high and the machine must be stopped or a catastrophic failure may occur.