UNCOUPLED AND TWIST-BEND COUPLED CARBON-GLASS BLADES FOR THE LIST TURBINE

Two different 9.2-m rotor blades that would be constructed of carbon and glass fiber-reinforced plastic composites – one with twist-bend coupling and one uncoupled – have been designed for Sandia National Laboratories’ stall-regulated LIST Turbine in Bushland, Texas. Both blades are derived from the prototype allglass NPS 9.2-m blade and maintain its outer contour. The results of dynamic simulations and structural analyses suggest that the use of carbon unidirectional fibers in the spar cap could reduce the weight of the NPS 9.2-m blade by approximately 37%, while the use of carbon fibers 20° off axis to induce twist-bend coupling could reduce the weight 31%. Both blade designs roughly halve the static moment of the baseline blade. Reductions of 40% in blade root edgewise bending moment fatigue are observed. The modest twist-bend coupling employed in the present design could reduce flapwise fatigue by as much as 6% at substall wind speeds. While this result may be confined to the low wind speed regime for a stall-regulated turbine, it is pertinent to the entire operating range of pitch-regulated turbines, which maintain blades operating substall. However, twist-bend coupling does not appear to reduce overall flapwise fatigue for stall-regulated turbines. Finally, altering the contour of the carbon/glass hybrid blades to produce designs with lower solidity and thinner sections might have produced greater coupling and flapwise fatigue reductions. The magnitudes of flapwise deflection and twist-bend coupling which can be introduced into the present design are limited by constraints on minimum material thickness resulting from the thick sections of the baseline blade.