Introduction to Wind Turbine Aerodynamics

276 Pages·2014·15.94 MB·English

by  A. P. Schaffarczyk (auth.)

Green Energy and Technology
A. P. Schaffarczyk
Introduction
to Wind
Turbine
Aerodynamics
Green Energy and Technology
For furthervolumes:
http://www.springer.com/series/8059
A. P. Schaffarczyk
Introduction to Wind Turbine
Aerodynamics
123
A.P.Schaffarczyk
Mechanical EngineeringDepartment
Universityof AppliedSciences
Kiel
Germany
ISSN 1865-3529 ISSN 1865-3537 (electronic)
ISBN 978-3-642-36408-2 ISBN 978-3-642-36409-9 (eBook)
DOI 10.1007/978-3-642-36409-9
Springer Heidelberg NewYork Dordrecht London
LibraryofCongressControlNumber:2014941105
(cid:2)Springer-VerlagBerlinHeidelberg2014
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This book is dedicated to my wife Ulrike and
our children Claudia, Carola and Kai
Foreword
The modern development of wind power is a remarkable story of the combined
effort of enthusiastic entrepreneurs and skilled engineers and scientists. Today,
wind power forms the most rapid advancing renewable energy resource with an
annual growth rate of about 30 %. Within the last 20 years the size of wind
turbines have increased from a rotor diameter of about 30 m to 150 m, corre-
spondingtoanincreaseinpowerbyafactorofmorethan25.Inthesameperiodof
time, the knowledge and scientific level of the aerodynamic research tools to
develop optimally loaded rotor blades have increased dramatically. Today, wind
turbine aerodynamicformsoneoftheresearchfrontiersinmodern aerodynamics.
The aerodynamics of wind turbines concerns modeling and prediction of the
aerodynamic forces on the solid structures of a wind turbine, and in particular on
the rotor blades of the turbine. Aerodynamics is the most central discipline for
predicting performance and loadings on wind turbines, and it is a prerequisite for
design,development, andoptimizationofwindturbines.From anoutsider’spoint
of view, aerodynamics of wind turbines may seem simple as compared to aero-
dynamics of, e.g., fixed-wing aircraft or helicopters. However, there are several
added complexities. Most prominently, aerodynamic stall is always avoided for
aircraft, whereas it is an intrinsic part of the wind turbines operational envelope.
Furthermore, wind turbines are subjected to atmospheric turbulence, wind shear
fromtheatmosphericboundarylayer,winddirectionsthatchangebothintimeand
in space, and effects from the wake of neighboring wind turbines. Introduction to
Wind Turbine Aerodynamics, written by an experienced teacher and researcher in
the field, provides a comprehensive introduction to the subject of wind turbine
aerodynamics. It is divided into ten chapters, each giving a self-contained intro-
duction to specific subjects within the field of wind turbine aerodynamics. The
book begins with an overview of different types of wind turbines, followed by a
comprehensive introduction to fluid mechanics, including different forms of the
basic fluid mechanical equations and topics such as potential flow theory,
boundary layer theory, and turbulence. The momentum theory, which still forms
the backbone in the rotor design of wind turbines, is presented in a separate
chapter, which, in a compressed form, describes the basic momentum theory as
well as the important blade-element momentum theory. State-of-the-art advanced
aerodynamic models are also presented. This includes vortex models as well as
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viii Foreword
ComputationalFluidDynamics(CFD)techniquesandanintroductiontothemost
common turbulence models. The last part of the book gives an overview of
experiments in wind turbine aerodynamics and the impact of aerodynamics on
bladedesign.Eachchaptercontainssomehomeworkproblemsandconcludeswith
abibliography.IntroductiontoWindTurbineAerodynamicsisahighlytopicaland
timely textbook of great value for undergraduate students as well as for trained
engineerswhowishtogetafastintroductionintothemanyaspectsoftheamazing
world of wind turbine aerodynamics.
Jens Nørkær Sørensen, Technical University of Denmark, Kongens Lyngby,
Denmark.
Copenhagen, April 2014 J. N. Sørensen
Preface
Wind Energy has flourished over the last 20 years. At the time of this writing,
approximately40 GWofwindpowerproductioncapacity,equivalentto80 billion
US $ in investment, is added to the worldwide energy portfolio annually.
About 2,40,000 (IEA Wind 2012 annual report) engineers are working in this
field, and many of them are confronted with challenges related to aerodynamics.
Even special academic programs (one of them being the M.Sc. Program in Wind
Engineering at the consortium of universities in Schleswig-Holstein, the north-
ernmostprovinceofGermany)nowareeducatingyoungpeopleinthisfield.From
personal experience, the author knows how difficult it is to navigate through the
jungle of scientific literature without being injured before having learned all the
basics.Thistextbookintendstohelpyoungandoldinterestedpeopletogaineasier
access to the basics of the fluid mechanics of wind turbines.
The scope of this book is to take the reader on an interesting journey from the
basics offluid mechanics to the design of wind turbine blades. The reader’s basic
knowledge of mathematics (Vector calculus) seems to be necessary for under-
standing, whereas fluid mechanics will be explained in what amounts to a crash
course.Butthereshouldbenomistake:fluidmechanicsbeingnon-linear,evenas
anappliedscience,isacomplicatedaffairandcanonlybelearnedandunderstood
byone’s ownproblemsolving.Thisisespeciallytruewheninvestigatingturbulent
flowwhichisofutmostimportancewheninvestigatingmechanical loadsonwind
turbine parts. Therefore, the estimated amount of effort necessary for solving our
selected problems at the end of each chapter ranges from 10 min to 10 months.
The author will try to give the beginning reader a glimpse of established
knowledgeabouttheaerodynamicsofwindturbines.Forthemorefamiliarreader,
thisbookwillfacilitatethediscoveryof(andhopefullyunderstandingof)relevant
advancedpapers.Inanyevent,allreaderswillgleanadeeperunderstandingwhich
will allow them to perform analyses either by hand or by using computer codes.
The structure is as follows: an introduction isgiven to inform the reader about
the specific relevance of wind turbine aerodynamics, while touching on some
interesting historical examples. Then a chapter on installed windmills and wind
turbines is added to describe the basics of mainstream and unconventional tech-
nology.Afterthatwe arereadytotackleourgeneralframework: thelaws offluid
mechanics.Iwilltrytolimitthecontentstothosetopicsthatarecloselyrelatedto
wind, understood as turbulent flow in the lower (boundary layer) part of the
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x Preface
atmosphere. Because the rotor swept area now easily reaches several hectares
ð¼104m2Þ something must be said about real-world inflow conditions, which are
notconstantfromaspatialortemporalpointofview. Chapter 5isthecoreofthe
book and explains the various versions of Momentum Theory as well as its limi-
tations,followedbyadescriptionofapplicationsofitscounterpart:VortexTheory.
After exhausting these classical methods, we then have to present the modern
approach of solving the differential equations called Computational Fluid
Dynamicsinsomedetail.Many effortshave beenexpendedoverthelast15years
to bridge the gap from older, sometimes called simpler, theories to actual mea-
surementsusingthesecomputationalmethods.Thisleadsdirectlytoatransitionin
thenextchaptertoadiscussionoffree-fieldandwindtunnelmeasurements.After
thatwewilltry toget evenclosertopractical,real things. Thismeansthatwe try
to give examples of actual blade shapes from industry. We conclude with sum-
marizing remarks and an overview of possible future developments.
As this text grew out of my lectures on wind turbine aerodynamics in the first
year of our international Master of Science Program, it is targeted toward this
student audience. Nevertheless, I have tried as much as possible to make it
valuable and informative for a much broader group of readers.
Kiel, Germany, April 2014 A. P. Schaffarczyk
Acknowledgments
I want to thank several people for introducing me to wind turbine aerodynamics:
first of all Sönke Siegfriedsen from aerodyn Energiesysteme GmbH, Rendsburg
and Gerard Schepers, ECN, the energy research center of the Netherlands, who
gave me a first chance in 1997. My very first contact with wind energy was
actually somewhat earlier (1993) during supervising a Diploma-Thesis which is
nowsummarizedasthestrangefarmerproblem(seeProblem5.1).Participationin
several IEA wind tasks (11, 20 and 29) gave me the opportunity to interact with
leading international experts. State of Schleswig-Holstein, Federal German and
European funding helped contribute to important projects and finally an Interna-
tional M.Sc. program inWindEngineering wasestablishedin2008inwhich now
more than 160 young people from all around the world (hopefully) learned about
wind energy technology.
Mr. Lippert prepared mostof the graphs and Mr. John Thayer brought the text
intomorecorrectEnglish.Anyerrors,however,aretheresponsibilityoftheauthor
only.
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