||Oil whirl is a common problem with journal bearings used on machines equipped with pressure lubrication systems operating at relatively high speeds. |
If the shaft is moved off center due to load, eccentricity, or imbalance, then the clearance on one side of the bearing will be greater than that on the other side.
As the lubricant rotates at less than 50% of shaft speed, it must squeeze through the narrow area where the shaft is closest to the bearing. The average speed of the lubricant increases inside the gap and slows down when it leaves the gap. Such a speeding up and slowing down process creates turbulence on both sides of the gap, and a vortex develops in the high-pressure lubricant zone.