The second example is the DU airfoils that were designed at DUT (Delft University of Technology) and tested in the DUT wind tunnel. These airfoil families have been successfully used in stall-regulated, variable-pitch, and variable-rpm wind turbines. Generally, the new airfoil families were designed such that the maximum lift coefficient is relatively insensitive to wall roughness. The first examples are the NREL nine airfoil families from the National Renewable Energy Laboratory (NREL) that were designed in 1995 for various rotors of horizontal-axis wind turbines (HAWTs) using the Eppler Airfoil Design and Analysis Code. In the past 20 years various airfoils have been designed especially for wind turbines.
Airfoil shapes code#
Compared with other inverse methods, the conformal mapping method was used in the Eppler code and it allowed the velocity distribution to be specified along the airfoil surface at different angles of attack. Using the conformal mapping method and the prescribed velocity distribution, the shape of the candidate airfoil was designed. Based on the pressure distribution, a potential velocity distribution was obtained. The philosophy of the design method is that a lift-drag polar was first defined according to the requirements of a designed airfoil and then a pressure coefficient distribution along the airfoil was deduced.
From the seventies of last century, NASA began on working with airfoil design using a code developed by Eppler and Somers. Introductionĭesign of airfoils for wind turbine blades is a very basic and important task for designing wind turbine rotors. Three new airfoils CQ-A15, CQ-A18, and CQ-A21 with a thickness of 15%, 18%, and 21%, respectively, are designed with the new integrated design method. In the optimization step, drag and lift force coefficients are calculated using the XFOIL code. As airfoil shapes are expressed with analytical functions, the airfoil surface can be kept smooth in a high degree. Using the trigonometric expression for airfoil profiles, a so-called integrated design method is developed for designing wind turbine airfoils. To validate and show the generality of the trigonometric expression, the profiles of the NACA 64418 and S809 airfoils are expressed by the present expression. As a direct consequence, three generic airfoil profiles are obtained from the expression. The characteristics of the coefficient parameters in the trigonometric expression for airfoils profiles are first studied.
Airfoil shapes series#
As a main component in the design method, airfoil profiles are expressed in a trigonometric series form using conformal transformations and series of polynomial equations. A new method for designing wind turbine airfoils is presented in this paper.
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