ABSTRACT
All definitions and necessary theory to understand the Blade Element Momentum (BEM) method have now been introduced. In this chapter the classical BEM model from Glauert (1935) will be presented. With this model it is possible to calculate the steady loads and thus also the thrust and power for different settings of wind speed, rotational speed and pitch angle. To calculate time series of the loads for time-varying input some engineering models must be added, as will be shown in a later chapter. In the 1-D momentum theory the actual geometry of the rotor – the number of blades, the twist and chord distribution, and the aerofoils used – is not considered. The Blade Element Momentum method couples the momentum theory with the local events taking place at the actual blades. The stream tube introduced in the 1-D momentum theory is discretized into N annular elements of height dr, as shown in Figure 6.1. The lateral boundary of these elements consists of streamlines; in other words there is no flow across the elements.
