Experimental Benchmarking of the Numerical Model of a Radial Lip Seal with a Surface Textured Shaft

A numerical study was conducted on radial lip seals running against shafts with deterministic surface structures and the results were compared to previously reported experimental results. For the experimental cases modeled, the lip seal operating conditions during oil drop testing were observed to be in full film lubrication with little or no contact. As such, a soft elastohydrodynamic (SEHL) model of the experiment was developed that uses the finite element (FE) method to determine contact conditions and structural deformation of the elastomer. The finite element model was also used to generate an influence coefficient matrix that is used in a coupled structural-fluid model. The fluid mechanics model is steady state and the mass conserving Jakobsson Floberg Olsson (JFO) cavition conditions are used to calculate the load-carrying capacity and the flow rate of the lubricant film. The potential impacts of two phenomena that are consistent with a steady-state model are also examined in this article. These are (1) the impact of the elastomer surface roughness on the results and (2) the impact of modeling the assembly process of the shaft into the seal (axial insertion of the shaft into the seal as opposed to a radial initial deformation assumption). The model agrees with the experimental results in the following ways: (1) the triangular surface asperity tends to pump oil toward its apex and the triangular surface cavity tends to pump oil toward its base; and (2) the surface asperity provides more load-carrying capacity and pumping effect than the surface cavity. The impact of transient effects such as the viscoelasticity and squeeze film dynamics are not included in the numerical model but are briefly discussed with regard to the discrepancy between the model and the experiment.