The Inuence of Aerodynamic Stall on the Performance of Vertical Axis Wind Turbines

241 Pages·2012·30.43 MB·English

The Influence of Aerodynamic Stall on the Performance of
Vertical Axis Wind Turbines
A Dissertation Submitted for the Degree of Doctor of Philosophy
by
Jonathan Mark Edwards
The University of Sheffield
Department of Mechanical Engineering
August 2012

Summary
There is currently an increasing desire for local small-scale sustainable energy generation. This
has lead to increased interest in the concept of the vertical axis wind turbine (VAWT), which is
potentiallywell-suitedtooperationwithinthebuiltenvironment.
This study investigates the performance and flow physics of a small-scale VAWT using
experimental and computational methods. The experiments utilise the University’s low-speed
open-section wind tunnel. The design and use of a variety of existing and newly developed
methods and apparatus is detailed, this includes the development of an entire VAWT-testing rig
and associated measurement equipment. Also included, is a new method for the experimental
determination of the power performance. A full performance curve is shown to be determined
usingashorttesttakingafewminutes.
The near-blade flow physics of the rotating blades were interrogated using particle image
velocimetry(PIV)aspartofameasurementcampaignwhichgoesbeyondtheexistingliterature
inboththerangeofmeasurementstakenandthesubsequentanalysiswhichispresented. Details
oftheeffectofchangesinazimuthalposition,tipspeedratioandfixingangleontheflowphysics
arepresented.
Comparable CFD simulations are first validated against the PIV measurements before they
are used to provide additional information for the performance analysis. A new methodology
for determining flowfield-corrected lift and drag polars from a CFD solution allows detailed
examinationoftheperformance-impactofthechangesintheaerodynamicforceswithazimuthal
positionandtipspeedratio.
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Described in this dissertation is work performed in the Department of Mechanical Engineering,
at the Univeristy of Sheffield between October 2008 and January 2012. I hereby declare that no
part of this work has been submitted as an exercise for a degree at this or any other university.
This dissertation is entirely the result of my own work and includes nothing which is the
outcome of collaboration, except where stated otherwise. This dissertation contains 163 figures
andapproximately60,000words.
-JonathanM.Edwards
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Acknowledgements
Firstly, I would like to thank my supervisor, Dr Rob Howell, for his guidance over the last three
years. HislevelofenthusiasmwasalwayshighandhissupportwasalwaystherewhenIneeded
it.
I also wish to thank the technicians of the Mechanical Engineering workshop. In particular,
Jeff for making the rotor and associated equipment, John and Dave for their work on the wind
tunnel, and Chris for his help with all of the electronic components. My thanks also go to Iain
and the technicians of the Electrical and Electronic Engineering workshop for manufacture of
thebladesandsupports.
The large amount of time spent stuck in the office was made considerably more pleasant by
thecompanyofGreg,Jason,Simon,NeilandJoe. AsecondopinionfromJoewasalwaysuseful,
and I appreciate the help he gave me on a variety of problems. In the lab, extra help was often
kindly provided by Louis, Dorit, Jon and Oke. Additional thanks for my remaining sanity go to
LizandmygoodfriendsinSheffieldforkeepingmeinorderoutsideofworkinghours.
Finally, I would like to thank my family for all the love and support that they have given me
overtheyears.
The University of Sheffield’s Studentship Program is gratefully acknowledged for providing the
necessaryfinancialsupportwhichenabledmetoundertakethisproject.
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DedicatedtomyDad
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