Rotor aerodynamics in sheared inflow : an analysis of out-of-plane bending moments

Abstract

A sheared wind profile creates an asymmetric wind field and an asymmetric wind turbine wake. Both of these have been described in the past but a study on their implications on the out-of-plane moment on the rotor is still a gap which needs to be addressed. A numerical assessment has been undertaken using a lifting-line free-wake vortex code. Owing to the lack of experimental validation, two other modelling approaches are used to assess the consistency of results - an actuator disc approach and a blade element momentum approach. Results were found to show acceptably good agreement. The line of action of the thrust force is found to be shifted by around 10% upwards above the rotor axis for the extreme shear case of α = 0.55. The wake was found to add to the asymmetry of the wind field by increasing the vertical shift in the line of action by 100% compared to the wind field alone. The results have important implications on the role of the out-of-plane bending moment on the wake kinematics as well as other issues related to fatigue performance of the rotor.