sin αst

LIST OF ATTACHMENTSROTOR THEORY
This project thesis uses the BEM method in calculation of steady state rotor performance
and in aerodynamic design of the rotor blades. The following equations describe the basics
of BEM analysis and form the foundation for the developed rotor design tool described in
appendix C. For a complete derivation of the formulas refer to [12, p. 91-153] and [46, p.
20-24], which are to be considered as sources for the following unless otherwise stated.
Further reference is made to the nomenclature of chapter 14 that contains the definitions
of symbols and subscripts.
Figure B.2 shows important velocities, angles and forces acting a ring element of the blade
profile.
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Figure B.2: Velocities, angles and forces on blade element
From figure B.2 it is evident that the angle of attack � is given by
And that the angle of relative wind � is given by
a and a’ refer to axial and tangential interference factors, respectively. For rotors with few
blades (B < 5) these are derived using the laws of conservation of momentum and angular
momentum
tan( �)
� = � � �
=
1 � a
1 � a'
V
r�
(B.1)
(B.2)