Wind Engineering
Module 5.1:
Wind Turbine Design Overview,
Radius, and Airfoils
Lakshmi N. Sankar
lsankar@ae.gatech.edu
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.
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.
Wind Turbine Design is an
Interdisciplinary Problem
Aerodynamics
Structures,
Structural Dynamics,
Vibrations, Stability,
Fatigue Life
Control systems for
RPM, Pitch, Yaw
Cost
Transmission,
gears, tower,
power systems,
etc.
Noise,
aesthetics
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.
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
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-50029439. Work performed by Global Energy Concepts, LLC, Kirkland, WA. Golden, CO:
National Renewable Energy Laboratory, June 2001.
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-50029950. 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).
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.
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
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.
Effect of rotor Radius on Total mass
Effect of Blade radius on Cost
including profit, overhead (28%)
Effect of Blade Radius on Tower Mass
Tower Cost = $1.50 per kg
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-r1280.pdf has a detailed catalog as well.
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
•
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
•
Main Airfoil Design Parameters
– Thickness, t/c
– Lift range for low drag and Clmax
– Reynolds number
– Amount of laminar flow
•
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
•
NREL Advanced Airfoil Families
Blade Length
Generator Size
Thickness
Airfoil Family
(meters)
(kW)
Category
(root--------------------------------tip)
1-5
2-20
thick
S823
5-10
20-150
thin
S804
S801
S803
5-10
20-150
thin
S807
S805A
S806A
5-10
20-150
thick
S821
S819
S820
10-15
150-400
thick
S815
S814
S809
S810
10-15
150-400
thick
S815
S814
S812
S813
15-25
400-1000
thick
S818
S816
S817
15-25
400-1000
thick
S818
S825
S826
S808
S822
Note: Shaded airfoils have been wind tunnel tested.
– Potential Energy Improvements
• NREL airfoils vs airfoils designed for aircraft (NACA)
•
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)
•
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