The blade element momentum (BEM) method

The current chapter presents the blade element momentum (BEM) method. The BEM method for a steady uniform inflow is presented in a first section. Some of the ad-hoc corrections that are usually added to the algorithm are discussed in a second section. An exception is made to the tip-loss correction which is introduced early in the algorithm formulation for practical reasons.

The ad-hoc corrections presented are: the tip-loss correction, the high-thrust correction (momentum breakdown) and the correction for wake rotation. The formulation of an unsteady BEM code is given in a third section. The dynamic effects discussed are the dynamic wake/inflow model, the yaw and tilt model, the dynamic stall model, and models for the interference of the tower and nacelle.

Some examples of steady and unsteady BEM simulations are given in a last section. The source code of a steady and unsteady BEM algorithm implemented in Matlab is given at the end of the chapter. The description of the BEM method includes the latest correction models that are derived and presented in Part IV.