Comparison of Spanwise Aerodynamic Loads Estimated from Measured Bending Moments Versus Direct Pressure Measurements on Horizontal Axis Wind Turbine Blades

Two methods can be used to determine aerodynamic loads on a rotating wind turbine blade. The first is to make direct pressure measurements on the blade surface. This is a difficult process requiring costly pressure instrumentation. The second method uses measured flap bending moments in conjunction with analytical techniques to estimate airloads. This method, called ALEST, was originallydeveloped for use on helicopter rotors and was modified for use on horizontal axis wind turbine blades. Estimating airloads using flap bending moments is much simpler and less costly because measurements can be made with conventional strain gages and equipment. This paper presents results of airload estimates obtained using both methods under a variety of operating conditions. Insights on thelimitations and usefulness of the ALEST bending moment technique are also included.