A simultaneous numerical solution for the lubrication and dynamic stability of noncontacting gas face seals

A numerical solution is presented for the dynamic analysis of gas lubricate d noncontacting mechanical face seals having a single grounded flexibly mou nted stator. Seal dynamics is solved in axial and angular modes of motion. Both the Reynolds equation and the equations of motion are arranged into a single state space form, allowing the fluid film lubrication and the dynami cs to be solved simultaneously. The resulting set of equations is solved us ing a high-order multistep ordinary differential equation solver, yielding a complete simulation for the seal dynamic behavior. Examples of seal motio n are given in detailed transient responses. The stability threshold is inv estigated to gauge the influence of seal parameters such as inertia, speed, coning, and the direction of sealed pressure drops. The results show two m odes of instability : (1) When the inertia effect is larger than a critical value, the natural response of the seal grows monotonically in a half-freq uency-whirl mode. (2) When the seal coning is less than some critical value in an outside pressurized seal, the minimum film thickness diminishes beca use of hydrostatic instability, and face contact occurs. Conversely. an ins ide pressurized seal is shown to be hydrostatically stable and have a super ior dynamic response at any coning.