Abstract
Lubrication plays a critical role in the effective performance of tapered roller bearings (TRBs) used as main bearings in wind turbines. Several experimental and CFD-based studies have investigated lubrication behavior in single-row TRBs. However, grease-lubricated double-row TRBs have not yet been studied extensively, particularly in large-size bearings. Therefore, this paper aims to investigate in detail the grease behavior in a tilted double-row TRB installed in a direct-drive wind turbine by developing a novel, three-dimensional, full-scale, multiphase CFD model. This model was implemented in the open-source environment OpenFOAM®, using a transient, incompressible, and multiphase solver based on the volume of fluid (VoF) model, where air and grease were treated as the two immiscible phases. Grease was modeled as a homogeneous non-Newtonian fluid using the Herschel–Bulkley formulation, with its rheological parameters determined by performing a best-fit analysis of experimentally obtained data. The simulated operating conditions included three grease filling ratios – 45 %, 35 %, and 21 % of the total volume of bearing lubricating chamber – at a rated rotational speed of 17.5 rpm, with a bearing tilt of 5° towards the main-frame side (MFS) relative to the vertical axis. The model captures grease distribution and inter-row fluxes across the bearing, identifying potential zones of lubricant starvation, and demonstrates how tilt affects grease flow between the two rows under varying fill conditions. Additionally, the model evaluates seal pressure, providing insights into the risk of grease leakage. The numerical predictions of grease distribution were validated experimentally using a smaller-scale TRB test rig, providing confidence in the model's ability to capture the dominant lubrication mechanisms in TRBs. The outcomes of this study have practical implications for optimizing relubrication strategies and improving maintenance planning for large wind turbine bearings.