Is blade element momentum theory (BEM) enough for smart rotor design

Smart rotor emerges as an innovation technique to reduce the impact of dynamic loading on wind turbines. Local movements of distributed aerodynamic devices will enhance the non-uniformity and dynamic effects of loading, which will challenge the applicability of the blade element momentum theory (BEM) for smart rotor control design due to its fundamental assumptions, quasi-steady state and independent annuli. From a recent report of Sandia Lab of field tests of wind turbine with trailing edge flaps, an unsteady aerodynamic model for the response to turbulent wind and AALC device actuation is needed and a dynamic wake model is necesary[1]. However, most of previous aeroseverelastic studies of smart rotor are based on BEM or BEM-based engineering dynamic inflow models, none of them verify the applicability of BEM for smart rotor study. In this paper, a free wake model which combined a vortex ring model with a semi-infinite cylindrical vortex tube is developed, and applied to an actuator disc with non-uniform and dynamic loading. After tested in a steady, uniform load case, the model is applied to three main load cases: a non-uniform steady load, a uniform dynamic load and a non-uniform dynamic load. Results from this model are compared with MT, and with two widely used engineering dynamic inflow models.