12/26/2023 0 Comments Naca 0015![]() ![]() The blade set design began with more » the definition of a family of three approximately 50% chord NLF sections (15, 18, and 21% t/c). This paper describes the design of this blade set. Sandia National Laboratories (SNL) is now in the process of procuring a blade set for its 17-m-diameter research turbine which will use NLF sections as blade elements. Studies have shown that vertical-axis wind turbines (VAWTs) using NLF sections as blade elements have the potential of producing energy at a significantly lower cost (approx. Natural laminar-flow (NLF) airfoils are those which can achieve significant extents of laminar flow (greater than or equal to 30% chord) solely through favorable pressure gradients. The 2-meter wind turbine model tests indicated that, with appropriate blade design, wood has potential for small vertical axis wind turbines. The thin NACA 0012 blade was excited into resonance well below the peak power rpm and constrained the turbine to low power output. The thicker NACA 0025 airfoil, more » where the thickness is 25 percent of the chord length, performed normally in the wind tunnel test. Two airfoil sections, NACA 0012 and NACA 0025, of 7.39 cm chord length (i.e., leading to trailing edge dimension) were shaped from curved laminated Lauan blanks which had the grain oriented along the blade arc. Although the tensile strengths of all candidate unidirectional laminates (Lauan, Monalava, poplar and maple) exceeded the induced blade stresses, Lauan was chosen for wind tunnel testing based on cost and dimensional stability. The manufacture, testing and tensile stress analysis of laminated wooden blades are described. The use of laminated Lauan plywood in a 2-meter-diameter, 3-bladed Darrieus wind turbine is described. Furthermore, the potential benefit of reducing the airfoil drag is clearly illustrated by the presentation of the individual contributions of lift and drag to power. The airfoil shapes considered are the conventional airfoils NACA 0018 and NACA 0021, and the SNLA 0018/50 airfoil designed at Sandia. To achieve this goal, the streamtube model of Paraschivoiu (1988) is used to predict the performance of VAWTs equipped with blades of various airfoil shapes. This technical brief illustrates the benefits and losses resulting from using NLF airfoils on VAWT blades. These features are similar to those of Natural Laminar Flow airfoils (NLF) and gave birth to the SNLA airfoil series. Objectives formulated for the blade profile were: modest values of maximum lift coefficient, low drag at low angle of attack, high drag at high angle of attack, sharp stall, and low thickness-to-chord more » ratio. As these blades were designed for aviation applications, Sandia National Laboratories developed a family of airfoils specifically designed for VAWTs in order to decrease the Cost of Energy (COE) of the VAWT (Berg, 1990). Most VAWTs currently operating worldwide use blades of symmetrical NACA airfoil series. The successful design of an efficient Vertical Axis Wind Turbine (VAWT) can be obtained only when appropriate airfoil sections have been selected. ![]()
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