Abstract

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 1.5 MW wind turbine. Lubrication is investigated across a “contact conditions dataset” generated by inputting processed loads, obtained from aeroelastic simulations, 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 starvation, grease thickener interactions and possible dynamic EHL effects. Results show that the modelled main-bearing would be expected to operate 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.

Highlights

  • IntroductionHigher than expected failure rates for wind turbine main-bearings have led to increased research focus on this component in recent years (Hart et al, 2019, 2020; Guo et al, 2021)

  • Results show that the modelled main-bearing would be expected to operate 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

  • It is first important to revisit the approximations made during modelling stages. This includes the half-space approximation for contacting surfaces, as well as the lubrication approximation applied in the same elastohydrodynamic lubrication (EHL) models

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Summary

Introduction

Higher than expected failure rates for wind turbine main-bearings have led to increased research focus on this component in recent years (Hart et al, 2019, 2020; Guo et al, 2021). The mechanisms leading to premature main-bearing failures are still not properly understood (Hart et al, 2019; Guo et al, 2021). It was concluded that axial motions are slow and highly unlikely to impact the lubricating film in these components This conclusion is valuable, in that it helps narrow down the possible causes of premature failures in main-bearings. A Hertzian contact model of a double-row spherical roller main-bearing was presented and used to investigate individual roller loads during operation. The total load resulting at the main bearing, which forms the input to the Hertzian contact model, is a vector containing the two radial and one axial (thrust) components

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