Calculation of Lubricated Rough Contact using OpenFOAM

In this work a lubricated rough contact model implemented inside the OpenFOAM framework is presented. Depending on the film thickness during lubrication four regimes are distinguished: thick film and thin film hydrodynamic, mixed and boundary lubrication regime. The lubricant flow is modeled using the Reynolds equation, a two-dimensional partial differential equation governing the lubricant pressure between two rough surfaces in relative motion. The Reynolds equation is discretized using the Finite Area Method, a two-dimensional counterpart of the Finite Volume Method, over a curved computational surface mesh. The asperity contact between asperities is calculated deterministically using the elastic-perfectly plastic contact model based on the procedure by Stanley and Kato and Sahlin et al. The calculation is performed using the elastic deflection approach and FFT method for fast calculation of the convolution integrals. The lubricant film temperature is calculated using a two--dimensional energy equation with an assumption of parabolic temperature profile across the film thickness. The surface temperatures are calculated using the moving heat source equation by Carslaw and Jaeger with the FFT numerical approach by Bos for faster calculation. The model takes into account non-Newtonian lubricant rheology and density-pressure dependence. The model is tested on two point contact test cases, in which ball-on-disc experiments are numerically simulated. The first test case uses Turbo T9 oil and is purely hydrodynamic. Two normal loads loads were considered, 38 and 154 N, and two entrainment speeds, 0.8 and 2 m/s. Friction coefficients calculated using the implemented model show a very good agreement with experimental results for all four cases. The second test case uses Turbo T68 oil and considers mixed and boundary lubrication regimes. Simulations were conducted for two rough ball specimens. For each specimen two types of roughness profiles were analysed: measured roughness profiles and approximated roughness profiles via sinus functions. For all cases, using a measured profile gave results closer to the experimental data. Generally, numerical results are in a fair agreement with experimental measurements.