Rural communities have a substantial and rapidly growing need for reliable, small-scale, wind power. This need cannot be filled without new and innovative designs that offer substantial improvements over the technologies currently available. The successful completion of this research will bring rural communities throughout the United States substantially closer to this goal. The purpose of this project is to develop a wind turbine blade design and manufacturing technique that results in a rotor system that costs less than $200 to manufacture, that will withstand 120 mile-per-hour winds,and that has a high efficiency, low start-up speed, and effective governing mechanism. OBJECTIVES: The product of the research will be a wind turbine rotor system design that can feasibly be manufactured for less than $200. An effective and reliable rotor system is fundamental to a wind turbine design that can be used successfully at rural locations with no power. The wind turbine can be markedted to three major customer bases: Rural agriculturalists who need power to optimize the productivity of their operation--as many as 43,000 projects in Wyoming alone; Rural homeowners--from 26% to 90%of potential rural home sites have nopower; and rural businesses who often need to power communication or computer equipment far from the power lines. APPROACH: Preliminary design parameters for a 6.8 KW rated Class II wind regime turbine will be established using a rated wind speed of 14 meters per second. The NREL design for 1 to 5 meter blades (patent 5,562,420) will be licensed and optimized for this particular application. Finite element analysis will be used to model and optimize a three-bladed design based on this patent. Optimization parameters will include low-wind-speed performance, high efficiency at low rotational speed, and high-wind-speed survivability. Optimization variables will include maximum chord length, tip speed ratio, pitch, and blade shape. When the aerodynamic optimization is complete, finite element analysis will again be used to analyze blade stresses and complete the detailed blade design and optimize manufacturing techniques. Methods of blade overspeed protection will then be optimized based on cost and reliability. After finalizing a manufacturing technique, a total manufacturing process will be evaluated on an economic basis. PROGRESS: 2004/05 TO 2004/12 It was determined that a farmstead-sized wind turbine should produce 600 Kwh per month in a 12 mph average wind speed. At 40% rotor efficiency and assuming reasonable mechanical efficiency a 12 foot rotor would be necessary. The design-point rotor speed was 300 rpm. 22 mph was chosen as the design wind speed. A blade profile was licensed from the National Renewable Energy Lab. The FLUENT computational fluid dynamics modeling program was leased to optimize the rotor system. Lift-to-Drag ratios were calculated. The optimum l/d ratio occurred at a wind angle of 6 deg for the tip and 7 deg for the root. An increase in wind angle resulted in a significant decrease in the l/d ratio-nearly 20% when the wind angle is increased from 6 to 9 deg. The model was compared to wind tunnel results for this blade profile. The wind tunnel data indicated much higher l/d ratios than the model results. The coefficients of drag calculated by the FLUENT model were significantly higher than the coefficients of drag measured in the wind tunnel. Using a transitional flow model the l/d ratios predicted were significantly closer to the experimental data suggesting that the discrepancy between model results and wind tunnel results could be explained to a degree by the effect of the transitional flow phenomena although the l/d ratios predicted by the transitional flow model were still closer to the FLUENT results than the experimental data. A program was written that allowed the research team to translate the rotor shape at any radius into an equation. To model the moving blades, a multiple reference frame model was used and tested until it was determined that the result of a run was independent of an artifact created in the mesh. Runs were made to optimize the lift coefficient, the blade twist, the blade taper, the point of transition between the root section and tip section, the shape of the transition, and the shape of the blade tip Iteratively until an optimum was found. At that point another parameter was optimized. The rotor system reached an efficiency of 43.9% and, since the incremental improvement with each parameter change reached a plateau, the team felt that a usable optimum had been reached. The concept of aero-elastic control is deceptively simple. Because of the orientation of the fibers a force on the blade causes the it to twist. The increased force of higher wind speeds will cause the blade angle of attack to increase, stalling the blade and slowing the rotor down. All components to slow the rotor could be eliminated. By building a composite with an asymmetric lay-up, it is possible to create a bending twisting couple in the material properties. Calculations predicted the twist obtained when a bending force was put on the blade. A blade was laid up by hand, using carbon fiber. Test results were consistent with the calculation. Because of the complexity, only a few production methods are possible. The blades could be laid up by hand at high cost and low productivity. Therefore, one of the resin transfer methods must be used. The cost of producing a rotor system was calculated to be $952. Glass fiber would lower the cost of the rotor system to $550. IMPACT: 2004/05 TO 2004/12 15.1 million rural homes and businesses can benefit from cheaper and more reliable electricity. The rural power grid can be more distributed and, therefore more reliable. Installation of small turbines can result in many rural jobs
