sin αst

6.3 Rotor performance
Aerodynamic rotor performance calculations are carried out using an iterative rotor de-
sign tool that has been developed as a part of this project on basis of the blade element
momentum (BEM) theory, described in appendix B.1. The rotor design tool enables calcu-
lation of aerodynamic flow conditions, forces, blade shape and rotor performance. It is
intended to be used by EWB in the development of future wind turbines and it is thus de-
signed with a spreadsheet interface that provides a certain degree of user-friendliness.
ROTOR
Details about the design tool, its functions, limitations and usage, can be found in appendix
C.
Performing analyses for a range of different wind speeds and rotational speeds enables the
rendering of rotor power curves that show rotor power output as a function of the rota-
tional speed. Figure 6.18 illustrates the power output for the developed rotor with a di-
ameter of 2.7 m at different wind speeds. Wind speeds are shown only up to 14 m/s, where
furling is initiated, see section 8.2.
Figure 6.18: Rotor power output as a function of rotational speed at wind speeds in the
range of 4 m/s to 14 m/s
The rotor power curves may be augmented to a system power curve by combining the
rotor power output of figure 6.18 with the linear characteristic of the generator, described
in section 7.1. An overlay plot of the rotor power output and the generator characteristic is
shown on figure 6.19.
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