Reason of angular wobble self-excited vibration and half frequency characteristic for gas film face seal

The angular wobbly self-excited vibration (AWs-EV) with the half-frequency of primary ring for fluids film face seal is an intrinsic property, which is similar to half-frequency whirl in journal bearings of hydrodynamic lubrication. Based on the continuity principle of fluids flow, a mechanism of explaining the generation of AWs-EV and the reason of the half-frequency characteristic are described.