Description and Computer Modeling of a Ball and Socket Hub That Enables Teetering for Three Bladed Wind Turbines

Abstract

A horizontal axis wind turbine with a ballandsocket hub is disclosed. The hub enables horizontal axis turbines with two or more blades to teeter in response to wind shear gradients. Computer modeling was done using existing and modified fast code in order to compare the new hub design with existing designs. Results show that a threebladed turbine with the ballandsocket hub provides very significant reductions in outofplane bending loads applied to the main shaft in comparison to a threebladed turbine with a rigid hub. Results also show that the new hub design provides significant reductions in the outofplane loads applied to the blades. A blade fatigue study using a rainflow counting of multiaxial torque contributions at the blade root was performed in order to assess the impact of these reductions, and results show that the threebladed turbine equipped with a ballandsocket, teetering hub provides for very significant reductions in lifetime blade damage in comparison to existing wind turbine designs due to a combination of factors. The first factor is that teetering largely eliminates the cyclic variations in outofplane torque on the blades that are observed with rigid hubs. Here, the fatigue study shows that the threebladed wind turbine with a teetering hub provides for an approximate sixfold reduction in lifetime blade damage in comparison to a threebladed turbine with a rigid hub. The second factor is that the addition of a third blade reduces the load on each blade by onethird. Here, the fatigue study shows that a threebladed turbine with a teetering hub provides for an approximate fourfold reduction in lifetime blade damage in comparison to a twobladed turbine with a teetering hub.