Airfoil design: Finding the balance between design lift and structural stiffness

Christian Bak, Nicholas Gaudern, Frederik Zahle, Tomas Vronsky

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Abstract

When upscaling wind turbine blades there is an increasing need for high levels of structural efficiency. In this paper the relationships between the aerodynamic characteristics; design lift and lift-drag ratio; and the structural characteristics were investigated. Using a unified optimization setup, airfoils were designed with relative thicknesses between 18% and 36%, a structural box height of 85% of the relative thickness, and varying box widths in chordwise direction between 20% and 40% of the chord length. The results from these airfoil designs showed that for a given flapwise stiffness, the design lift coefficient increases if the box length reduces and at the same time the relative thickness increases. Even though the conclusions are specific to the airfoil design approach used, the study indicated that an increased design lift required slightly higher relative thickness compared to airfoils with lower design lift to maintain the flapwise stiffness. Also, the study indicated that the lift-drag ratio as a function of flapwise stiffness was relatively independent of the airfoil design with a tendency that the lift-drag ratio decreased for large box lengths. The above conclusions were supported by an analysis of the three airfoil families Riso-C2, DU and FFA, where the lift-drag ratio as a function of flapwise stiffness was decreasing, but relatively independent of the airfoil design, and the design lift coefficient was varying depending on the design philosophy. To make the analysis complete also design lift and lift- drag ratio as a function of edgewise and torsional stiffness were shown.
Original languageEnglish
Article number012017
Book seriesJournal of Physics: Conference Series (Online)
Volume524
Number of pages10
ISSN1742-6596
DOIs
Publication statusPublished - 2014
Event5th International Conference on The Science of Making Torque from Wind 2014 - Technical University of Denmark, Copenhagen, Denmark
Duration: 10 Jun 201420 Jun 2014
Conference number: 5
http://indico.conferences.dtu.dk/conferenceDisplay.py?confId=138

Conference

Conference5th International Conference on The Science of Making Torque from Wind 2014
Number5
LocationTechnical University of Denmark
CountryDenmark
CityCopenhagen
Period10/06/201420/06/2014
Internet address

Bibliographical note

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