Investigation of the validity of the Blade Element Momentum Theory for wind turbine simulations in turbulent inflow by means of Computational Fluid Dynamics

In this work three different numerical methods are used to simulate a MW class wind turbine under turbulent inflow conditions. These methods are a blade resolved Computational Fluid Dynamics (CFD) simulation, an actuator line based CFD simulation and a Blade Element Momentum (BEM) approach. For all three methods sectional and integral forces are investigated in terms of mean, standard deviation, power spectral density and fatigue loads. It is shown that the power spectral densities of integral forces are in good agreement in the low frequency range for all methods. However, deviations are observed from 2 Hz onward. Although the fatigue loads of the CFD based methods are similar for the torque, the loads from BEM differ by 22%. For the thrust BEM only deviates by 4.5% from the blade resolved case. Nevertheless the actuator line based simulation differs by up to 7.3%. The standard deviations of sectional forces for all three methods relate very well to the standard deviation of integral forces. Nevertheless, a similar relation for the fatigue loads could not be observed.