Rotorwhirl

Rotorwhirl is a term used in rotor dynamics to refer to a sustained whirling or precessional motion of a rotating shaft or rotor relative to its housing. The phenomenon arises from dynamic instability in bearing and stiffness interactions, and is typically observed in high-speed machines with limited damping or residual misalignment. The term combines "rotor" and "whirl," highlighting its rotor-centric origin.

Causes include unbalance forces, clearances in bearings, misalignment, and gyroscopic effects that couple lateral and torsional modes. When the energy input sustains a lateral motion at or near one of the rotor's critical speeds, the whirl amplitude may grow, potentially locking into a periodic orbit or displaying complex, quasi-periodic behavior. Damping and stiffness variation influence the stability margin and the type of whirl observed.

Industries with rotorwhirl risk include turbomachinery, flywheels, precision spindles, and aerospace actuators. Detection relies on vibration monitoring, orbit analysis, and resonance tracing, while mitigation draws on balancing, bearing redesign, added damping, stiffening, and, in some cases, active vibration control. Proper alignment and clearance management are also essential to reduce susceptibility to whirl.

In rotor dynamics literature, rotorwhirl is related to broader concepts of forward and backward whirl, critical speeds, and Campbell diagrams. It is distinguished from random vibration by its characteristic whirling patterns and often predictable onset under certain operating conditions. The term remains a descriptive shorthand rather than a fixed technical category in all contexts.