Wind turbine main-bearing lubrication - part 2: simulation based results for a double-row spherical roller main-bearing in a 1.5 MW wind turbine

This paper is the second in a two-part study on lubrication in wind turbine main-bearings. Where "Part 1" provided an introductory review of elastohydrodynamic lubrication theory, this paper will apply those ideas to investigate lubrication in
the double-row spherical roller main-bearing of a 1.5MWwind turbine. Lubrication is investigated across a "contact conditions dataset" generated by inputting main-bearing applied loads, estimated from hub loads generated using aeroelastic simulation software, into a Hertzian contact model of the main-bearing. From the Hertzian model is extracted values of roller load and contact patch dimensions, along with the time rate-of-change of contact patch dimensions. Also included in the dataset are additional environmental and operational variable values (e.g. wind speeds and shaft rotational speeds). A suitable formula for estimating film thickness within this particular bearing is then identified. Using lubricant properties of a commercially available wind turbine grease, specifically marketed for use in main-bearings, an analysis of film thickness across the generated dataset is undertaken. The analysis includes consideration of effects relating to temperature, starvation, grease thickener interactions and possible non-steady effects. Results show that the studied main-bearing is at risk of operating under mixed lubrication conditions for a non-negligible proportion of its operational life, indicating that further work is required to better understand lubrication in this context and implications for main-bearing damage and operational lifetimes. Key sensitivities and uncertainties within the analysis are discussed, along with recommendations for future work.