Roughness induced variation as a new mechanism for hydrodynamic lubrication between parallel surfaces

This work proposes a new lift mechanism capable of explaining the hydrodynamic lift observed in real mechanical face seals with parallel surfaces. While it is well established that roughness is a key factor inducing such lift, its effect is commonly explained in the form of micro-wedges and asperity-level cavitation. The novelty of this work is to consider roughness induced random variability in the flow restriction, which induces effective wedges. First, a dedicated stochastic two-scale model is developed and used to demonstrate the proposed new mechanism in a case study. We demonstrate that the described new mechanism acts at scales comparable to the macroscopic size of the seal, much larger than the commonly considered micro-wedges. Afterwards, the limitations for this new proposed mechanism are discussed.