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  • 1. Wind Engineering Module 5.1: Wind Turbine Design Overview, Radius, and Airfoils Lakshmi N. Sankar [email_address]
  • 2. Recap
    • In Module 1, we looked at an overview of the course objectives, syllabus, and deliverables. We also reviewed history of wind technology, nomenclature, and case studies.
    • In Module 2, we looked at the wind turbine as an actuator disk, and established the theoretical maximum for power that may be captured.
    • In module 3, we reviewed airfoil aerodynamics, and discussed how to compute lift and drag coefficients. We also reviewed airfoil design issues.
    • In Module 4, we looked at how wind turbines may be modeled using blade element theory. We also looked at some commonly available public domain performance codes.
  • 3. Overview
    • In this module, we will look at how to design wind turbines.
    • This study is purely from an aerodynamic perspective.
    • In practice, wind turbine design is a multidisciplinary optimization problem.
    • Unlike wind turbine analysis, there are no unique solutions to a design problem.
      • This is why wind turbines from various manufacturers look different.
  • 4. Wind Turbine Design is an Interdisciplinary Problem Aerodynamics Structures, Structural Dynamics, Vibrations, Stability, Fatigue Life Control systems for RPM, Pitch, Yaw Transmission, gears, tower, power systems, etc. Cost Noise, aesthetics
  • 5. Parameters to be Chosen
    • We need to decide on
      • Number of blades
      • Blade planform (i.e. how does chord vary with radius)?
      • Blade radius
      • Blade twist distribution
      • Airfoils
      • RPM
      • Decisions about variable RPM, variable pitch
    • We need to consider cost, noise, vibrations, fatigue, etc as well.
  • 6. Starting Point
    • Before starting a design, it is a good idea to survey existing concepts and collect data.
    • Learn from other designers’ experience and success, and mistakes.
    • While much of the information for commercial systems is proprietary, there are good public resources.
      • http://www.nrel.gov/wind/publications.html
  • 7. Some References cited in NREL/TP-500-40566
    • [1] Harrison, R.; Jenkins, G.; Cost Modeling of Horizontal Axis Wind Turbines. ETSU W/34/00170/REP. University of Sunderland, School of Environment, December 1993
    • [2] Griffin, D. A. WindPACT Turbine Design Scaling Studies Technical Area 1 -- Composite Blades for 80- to 120-Meter Rotor; 21 March 2000 - 15 March 2001. NREL/SR-500-29492. Golden, CO: National Renewable Energy Laboratory, April 2001.
    • [3] Smith, K. WindPACT Turbine Design Scaling Studies Technical Area 2: Turbine, Rotor and Blade Logistics; 27 March 2000 - 31 December 2000. NREL/SR-500-29439. Work performed by Global Energy Concepts, LLC, Kirkland, WA. Golden, CO: National Renewable Energy Laboratory, June 2001.
  • 8. References (Continued)
    • [4] WindPACT Turbine Design Scaling Studies Technical Area 3 -- Self-Erecting Tower and Nacelle Feasibility: March 2000 - March 2001. (2001). NREL/SR-500-29493. Work performed by Global Energy Concepts, LLC, Kirkland, WA. Golden, CO: National Renewable Energy Laboratory, May 2001.
    • [5] Shafer, D. A.; Strawmyer, K. R.; Conley, R. M.; Guidinger, J. H.; Wilkie, D. C.; Zellman, T. F.; Bernadett, D. W. WindPACT Turbine Design Scaling Studies: Technical Area 4 -- Balance-of-Station Cost; 21 March 2000 - 15 March 2001. NREL/SR-500-29950. Work performed by Commonwealth Associates, Inc., Jackson, MI. Golden, CO: National Renewable Energy Laboratory, July 2001.
    • [6] Malcolm, D. J.; Hansen, A. C. WindPACT Turbine Rotor Design Study: June 2000--June 2002 (Revised). NREL/SR-500-32495. Work performed by Global Energy Concepts, LLC, Kirkland, WA; and Windward Engineering, Salt Lake City, UT. Golden, CO: National Renewable Energy Laboratory, April 2006 (revised).
  • 9. References (Continued)
    • [7] Poore, R.; Lettenmaier, T. Alternative Design Study Report: WindPACT Advanced Wind Turbine Drive Train Designs Study; November 1, 2000 -- February 28, 2002. NREL/SR-500-33196. Work performed by Global Energy Concepts, LLC, Kirkland, WA. Golden, CO: National Renewable Energy Laboratory, August 2003.
    • [8] Bywaters, G.; John, V.; Lynch, J.; Mattila, P.; Norton, G.; Stowell, J.; Salata, M.; Labath, O.; Chertok, A.; Hablanian, D. Northern Power Systems WindPACT Drive Train Alternative Design Study Report; Period of Performance: April 12, 2001 to January 31, 2005. NREL/SR-500-35524.
  • 10. Design Approaches
    • A parametric sweep may be done using a fast but reliable software such as WT_PERF or PROPID to identify best configurations and parametric combinations.
    • One can pose the problem as an optimization problem: maximize power (MW) or MW-Hr for a range of wind conditions, subject to constraints such as cost, weight, fatigue life, etc.
      • PropID has an inverse mode that accomplishes this.
    • One can use genetic algorithms to combine the best features of known configurations (gene pool).
      • PropGA developed by Philippe Giguère
  • 11. Which parameters to change?
    • Rotor radius affects peak power.
      • Recall actuator disk theory says that the power is proportional to disk area.
    • Changing the twist changes the angle of attack and affects lift and drag coefficient.
    • Changing the chord affects the axial induction factor, and to a small extent the tangential induction factor.
      • The goal is to make axial induction factor approach the Betz limit.
    • Caution: The rotor performance is affected by the interplay between these variables.
  • 12. Effect of rotor Radius on Total mass
  • 13. Effect of Blade radius on Cost including profit, overhead (28%)
  • 14. Effect of Blade Radius on Tower Mass Tower Cost = $1.50 per kg
  • 15. Airfoils
    • There are several to choose from.
    • You may design your own as well, using Module 3 material, as you gain experience in this field.
    • Dan Somers’ web site is a valuable resource.
      • http://www.airfoils.com/
    • Prof. Selig at UIUC has an excellent database as well.
      • http://www.ae.uiuc.edu/m-selig/ads/coord_database.html
    • http://www.risoe.dk/rispubl/VEA/veapdf/ris-r-1280.pdf has a detailed catalog as well.
  • 16. Wind Turbine Airfoils
    • Design Perspective
      • The environment in which wind turbines operate and their mode of operation not the same as for aircraft
        • Roughness effects resulting from airborne particles are important for wind turbines
        • Larger airfoil thicknesses needed for wind turbines
      • Different environments and modes of operation imply different design requirements
      • The airfoils designed for aircraft not optimum for wind turbines
    The remaining slides are from a short course on PropID at UIUC Prepared by Jim Tangler: http://www.ae.uiuc.edu/m-selig/propid/shortcourse99/Material.html
  • 17.
    • Design Philosophy
      • Design specially-tailored airfoils for wind turbines
        • Design airfoil families with decreasing thickness from root to tip to accommodate both structural and aerodynamic needs
        • Design different families for different wind turbine size and rotor rigidity
  • 18.
    • Main Airfoil Design Parameters
      • Thickness, t/c
      • Lift range for low drag and C lmax
      • Reynolds number
      • Amount of laminar flow
  • 19.
    • Design Criteria for Wind Turbine Airfoils
      • Moderate to high thickness ratio t/c
        • Rigid rotor: 16%–26% t/c
        • Flexible rotor: 11%–21% t/c
        • Small wind turbines: 10%-16% t/c
      • High lift-to-drag ratio
      • Minimal roughness sensitivity
      • Weak laminar separation bubbles
  • 20.
    • NREL Advanced Airfoil Families
    Note: Shaded airfoils have been wind tunnel tested.
  • 21.  
  • 22.  
  • 23.  
  • 24.  
  • 25.
      • Potential Energy Improvements
        • NREL airfoils vs airfoils designed for aircraft (NACA)
  • 26.
    • Other Wind Turbine Airfoils
      • University of Illinois
        • SG6040/41/42/43 and SG6050/51 airfoil families for small wind turbines (1-10 kW)
        • Numerous low Reynolds number airfoils applicable to small wind turbines
      • Delft (Netherlands)
      • FFA (Sweden)
      • Risø (Denmark)
  • 27.
    • Airfoil Selection
      • Appropriate design Reynolds number
      • Airfoil thickness according to the amount of centrifugal stiffening and desired blade rigidity
      • Roughness insensitivity most important for stall regulated wind turbines
      • Low drag not as important for small wind turbines because of passive over speed control and smaller relative influence of drag on performance
      • High-lift root airfoil to minimize inboard solidity and enhanced starting torque