The rotary lip seal is the most widely used dynamic seal. It is used extensively in the automotive and appliance industries. Experimentally, it is well known that the microasperities on the shaft surface can significantly affect the performance of a lip seal, even though the shaft roughness, after run-in, is much smaller than the lip roughness. In the present study, several deterministic numerical models are developed to investigate the effect of shaft surface finish on rotary lip seal behavior, through an understanding of the basic physics of lip seal operation. This project is performed in a step by step manner with gradually increasing complexity. Four models are included in this study: hydrodynamic analysis, elastohydrodynamic analysis for full film lubrication, mixed-EHL model for mixed lubrication with asperity contact, and transient dynamic mixed-EHL model for startup and shutdown processes. Those analyses allow the examination of some important seal characteristics, such as the load support sharing between hydrodynamic and contact pressure, contact and cavitation area ratio, reverse pumping rate, liftoff speed for tracing the liftoff process and average film thickness. The development of fluid, contact and cavitation areas as a result of the changing operation condition is also examined. The results of the present deterministic modeling indicate that shaft surface roughness can produce significant desirable effects on lip seal behavior. An appropriate shaft surface profile could improve the sealing ability and prevent seal failure.

A thorough investigation on the existing hydrodynamic lubrication theories and the reverse pumping theories for the conventional lip seal is conducted. On that basis, the algorithms and the methods used in the numerical modeling of the conventional lip seal are modified and applied to the study of the lip seal running against surface textured shafts. For each step of the study, the numerical model is benchmarked against the experimental results. Important physical mechanisms which explain the reverse pumping ability of the triangular surface structures are revealed. Meanwhile, the accuracy of the numerical model is tested. In general, the numerical simulation results match the experimental observation well. However, there are several important discrepancies. For each discrepancy the possible causes are discussed, which benefits the further attempts of the modeling work on the lip seal running against surface textured shafts. The conclusions of this study themselves can be used as a guidance to the design of the surface textured shafts for the lip seal applications. Finally the limitation of the current theories and the modeling methods are discussed and reasonable improvements which can be done are proposed for the future work.