Passive Control of a Wind Turbine Blade Using Composite Material

Abstract

The weight and the cost of a wind turbine are two important factors that make wind energy competitive with other energy sources. The weight of the rotor is typically 40–80% of the total weight of the system. Thus, lowering cost by reducing the weight of the blade is an important consideration. Another significant factor is the operational life of the machine. At present, a wind turbine’s life span is about 108 cycles or 20 years of continuous service. Innovative design solutions are needed in order to meet the criteria of improved stiffness, fatigue life, reliability, and efficiency. The directional property of an anisotropic composite material can be used to passively control wind turbine blade geometry in fluctuating wind speeds. Anisotropic materials show various levels of elastic coupling, based upon the ply angle in the layers. Structural behavior that exhibits both bending and twisting due to a pure bending load is known as twist-bend coupling. This type of behavior can be used for load reductions, particularly fatigue loads. The idea is to allow the blade to unload (reducing the speed) by allowing the wind induced bending moment to twist the blade. Increments in bending moment produce an increment in the twist that lowers the aerodynamically produced load. Higher blade stiffness can be achieved by full or partial replacement of glass fiber with carbon fiber. Carbon fibers are not used extensively on commercial wind turbine blades as they are more costly than glass fiber. The main objectives of this work are: (1) design a baseline model (made from glass fibers) of the wind turbine blade in accordance with published airfoil data; (2) conduct a finite element analysis of the blade and determine stresses, and strain within the blade; (3) develop a hybrid blade design by replacing the glass fibers with carbon fibers in the spar cap; and (4) validate the feasibility of implementing bend-twist coupling in the wind turbine blade by studying stresses, and strain behavior. By giving different orientation in the carbon fiber and changing the fiber layer, different designs are analyzed with regard to the above listed criteria.