CONSIDERATIONS OF GRAVITY EFFECTS ON VAWT ROTOR CONFIGURATIONS WHICH MINIMIZE FLATWISE MOMENTS AND STRESSES

Anticipating that composite materials will permit greater freedom when future VA WT1 rotor blades are configured, this paper further examine s the benefits of adopting true Troposkien shapes for blades which do not use horizontal struts. Two parameters are identified which control blade geometry under combined rotational and gravitational loads. Rep resentative zero-bending-moment shapes are calculated, both for consta nt mass distribution and for several new variable-mass families. The l atter include one case whose mathematical solution proves remarkably s imple. Steady design stresses are found to be severely affected by dev iations from the ideal shape. The concept of ''aerodynamic Troposkien, '' which preserves zero bending moments in the presence of 1-P cyclic normal forces, is extended to account for gravity as well as inertial effects on blade shape. This concept is limited to unstalled flow and it is found to require unrealistic blade chord distributions near the tower when gravity effects are included. It is noted that both steady gravitational loads and nonsteady aerodynamic normal force loads will become increasingly important in achieving high-cycle fatigue life wi th larger-scale rotor blades. It is indicated that this achievement wi ll depend primarily on configuring the rotor blades to minimize the cy clic flatwise bending moments and stresses due to the nonsteady normal forces.