Load distribution in a roller-type rotor blade bearing

Pitch bearings of wind turbines are large, grease-lubricated rolling bearings that connect the rotor blades with the rotor hub. Rolling bearings are the standard bearing type for this application. Most blade bearings are four-point bearings with one or two rows. Three-row roller bearings with two axial rows and one radial row have higher costs, but are an increasingly used alternative. Both rotor blade and rotor hub have a varying stiffness along the circumference of the bearing rings. This results in rotationally non-symmetric load sharing (load distributions) of the bearing rollers. The load distribution depends on the pitch angle, the load magnitude and the load angle. In this paper, we evaluate the load sharing of such a three-row bearing for a reference wind turbine of the 3 MW-class, taking account of the stiffness of the interface parts hub and rotor blade. A set of finite-element simulations with varying loads, load angles and pitch angles has been executed to determine the influence of the named parameters on the loads of the individual rollers. Curve fits of these discrete load points allow the determination of roller loads for any given parameter combination. One application of the results is the determination of the overall bearing load which is a key input for fatigue lifetime calculations.