Wind Engineering Module 5.1: Wind Turbine Design Overview, Radius, and Airfoils

1
Wind EngineeringModule 5.1 Wind Turbine Design
Overview, Radius, and Airfoils

• Lakshmi N. Sankar
• lsankar_at_ae.gatech.edu

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
Structures, Structural Dynamics, Vibrations,
Stability, Fatigue Life
Transmission, gears, tower, power systems, etc.
Aerodynamics
Noise, aesthetics
Control systems for RPM, Pitch, Yaw
Cost
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 Costincluding profit,
overhead (28)
14
Effect of Blade Radius on Tower MassTower 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/shortcourse
99/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 Clmax
• Reynolds number
• Amount of laminar flow

19

• Design Criteria for Wind Turbine Airfoils
• Moderate to high thickness ratio t/c
• Rigid rotor 1626 t/c
• Flexible rotor 1121 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
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
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