The AVATAR project aims to improve aerodynamic and fluid-structure models for large 10MW wind turbines by validating submodels against experiments. These include airfoil measurements in a pressurized wind tunnel up to Reynolds numbers of 15 million. A blind test was conducted comparing experimental and computational results. The project also involves designing an advanced 10MW AVATAR reference wind turbine with longer blades, higher tip speed and lower induction compared to a conventional design.

1. www.eera-avatar.eu
This project has received funding from the European Union’s Seventh Programme for research, technological development and
demonstration under grand agreement No FP7-ENERGY-2013-1/n° 608396 .
AVATAR project
Advanced Aerodynamic Tools for lArge Rotors
Gerard Schepers
2016 Wind Turbine Blade Workshop
Sandia National Laboratories, USA
August 31st, 2016

2. FP7-ENERGY-2013-1/ n° 608396 2
List of Contents
q Introduction into the project
q Design of AVATAR Reference Wind Turbine 1)
q Aerodynamics at high Reynoldsnumbers
• Airfoil measurements in pressurized DNW-HDG tunnel 2)
q Aero-elasticity of large turbines at yaw
• BEM versus free vortex wake aerodynamic modelling3)
19-09-16
1) Acknowledgement G. Sieros, M. Stettner
2) Acknowledgement O. Ceyhan, O. Pires
3) Acknowledgement K. Boorsma, S. Voutsinas
And all other project partners!

3. FP7-ENERGY-2013-1/ n° 608396 3
EU FP7 Project initiated by EERA
1. Energy Research Centre of the Netherlands,ECN (Coordinator)
2. Delft University of Technology,TUDelft
3. Technical University ofDenmark, DTU
4. Fraunhofer IWES
5. University of Oldenburg,Forwind
6. University of Stuttgart, USTUTT
7. National Renewable Energy Centre,CENER
8. University of Liverpool/University ofGlasgow, ULIV/UoG
9. Centre for Renewable Energy Sources and Saving,CRES
10.National Technical University ofGreece, NTUA
11.Politecnico di Milano,Polimi
12.GE Global Research,Zweigniederlassung der General Electric Deutschland Holding GmbH,GE
13.LM Wind Power, LM
19-09-16

4. FP7-ENERGY-2013-1/ n° 608396 4
Period
• Project period:
November 1st 2013- November 1st 2017

5. FP7-ENERGY-2013-1/ n° 608396 5
Main motivation for AVATAR:
Aerodynamics of large wind turbines (10-20MW)
• We simply don’t know if present aerodynamic models are good
enough to design 10MW+ turbines
• 10MW+ rotors violate assumptions in current aerodynamic tools,
e.g.:
– Reynolds number effects,
– Compressibility effects
– Thick(er) airfoils
– Flow transition and separation,
– (More) flexible blades
– Flow devices
• Hence 10MW+ designs fall outside the validated range of
current state of the art tools.
19-09-16

6. FP7-ENERGY-2013-1/ n° 608396 6
Avatar: Main objective
To bring the aerodynamic and fluid-structure models to a
next level and calibrate them for all relevant aspects of
large (10MW+) wind turbines
19-09-16

7. FP7-ENERGY-2013-1/ n° 608396 7
Avatar: Work procedure
– Problem: No 10 MW turbines are on the market yet for validation
– Hence: Validate submodels against experiments
• Pressurized HDG tunnel of German Dutch Wind Tunnel facilities (DNW)
• Airfoil measurements at Reynolds numbers up to RE = 15 M and
low Mach (< 0.2)
• LM: Wind tunnel airfoil measurements
• Forwind: Wind tunnel airfoil measurements at representative turbulence
• TUDelft: Wind tunnel experiments on airfoils with vortex generators, flaps
• NTUA: Wind tunnel experiments on airfoils with/without vortex generators
• DTU : Danaero: Aerodynamic field experiments on a 2.3 MW turbine and
supporting 2D wind tunnel measurements
19-09-16

8. FP7-ENERGY-2013-1/ n° 608396 8
Avatar: Work procedure
Use the different models from partners in the project
o It is a cooperation project!
o In the project we have many models which range from computational
efficient ‘engineering’ tools to high fidelity but computationally expensive
tools
o Engineering tools are needed in industrial design codes 1)
o High fidelity models (and intermediate models) feed information towards
engineering models
19-09-16
1
) J.G. Schepers ‘Engineering models in wind energy aerodynamics,’ (2012).
http://repository.tudelft.nl/islandora/object/uuid:92123c07-cc12-4945-973f-103bd744ec87/?collection=research

9. FP7-ENERGY-2013-1/ n° 608396 9
Avatar: Work procedure
• Demonstrate the value of the improved tools on 10 MW
reference rotors with and without flow control devices
1. INNWIND.EU reference rotor (more or less conventional
design philosophy)
2. AVATAR reference rotor which should be more
challenging from an aerodynamic point of view (e.g.
lower induction, longer, more slender blades, thicker
airfoils, higher tip speed).
• Compare results from ‘old’ and improved models at the end
of the project

10. FP7-ENERGY-2013-1/ n° 608396 10
List of Contents
q Introduction into the project
q Design of AVATAR Reference Wind Turbine 1)
q Aerodynamics at high Reynoldsnumbers
• Airfoil measurements in pressurized DNW-HDG tunnel
q Aero-elasticity of large turbines at yaw
• BEM versus free vortex wake aerodynamic modelling
19-09-16
1) Acknowledgement G. Sieros, M. Stettner

11. AVATAR RWT
Power: 10 MW 10 MW
Rotor diameter: 178.3m 205.8m
WTPD: 400 W/m2 300 W/m2
Axial induction: 0.3 0.24
RPMàTip speed 9.8rpmà 90m/s 9.8 à103.4 m/s
Hub height: 119m 132.7m

12. FP7-ENERGY-2013-1/ n° 608396
Classical Approach versus Low Induction
• Power Coefficient flat around Betz
maximum (a = 1/3)
• Aerodynamic load coefficient strongly
dependant on a
• Increase diameterà maintain
aerodynamic loadsà increase power
2
3
)1(4
2
1
aa
AU
P
CP ==
0
0.2
0.4
0.6
0.8
1
1.2
0 0.1 0.2 0.3 0.4 0.5 0.6
Cdax
Cp
)1(4
2
1
.
2
. aa
AU
axD
C axD ==
a[-]

13. FP7-ENERGY-2013-1/ n° 608396 13
Design of AVATAR RWT
• 5% Increase in energy production due to larger diameter
• Key rotor load levels are maintained
• Non-rotor loads exceededà Redesign of AVATAR rotor at end of project
• Note: LCOE of AVATAR turbine assessed
in 1) taking into account additional
advantage of lower wake effects
1) R. Quinn, B. Bulder, J.G. Schepers
A parametric investigation into the effect of low induction
rotor (LIR) wind turbines on the LCoE of a 1GW offshore wind
farm in a North Sea wind climate, EERA-Deepwind 2016

14. FP7-ENERGY-2013-1/ n° 608396
Design of AVATAR RWT
• The operational conditions
Section Thickness Re (rated) Ma (rated) Re (Min) Ma (Min)
60.0% 7.0×106 0.05 4.4×106 0.03
40.1% 11.0×106 0.07 7.0×106 0.05
35.0% 14.0×106 0.09 9.0×106 0.06
30.0% 17.0×106 0.12 10.0×106 0.07
24.0% 20.0×106 0.16 12.0×106 0.10
24.0% 16.0×106 0.25 11.0×106 0.15
24.0% 13.0×106 0.30 8.0×106 0.18
21.0% 20.0×106 0.16 12.0×106 0.10
21.0% 16.0×106 0.25 11.0×106 0.15
21.0% 13.0×106 0.30 8.0×106 0.18
Section Thickness Re (rated) Ma (rated) Re (Min) Ma (Min)
60.0% 7.0×106 0.05 4.4×106 0.03
40.1% 11.0×106 0.07 7.0×106 0.05
35.0% 14.0×106 0.09 9.0×106 0.06
30.0% 17.0×106 0.12 10.0×106 0.07
24.0% 20.0×106 0.16 12.0×106 0.10
24.0% 16.0×106 0.25 11.0×106 0.15
24.0% 13.0×106 0.30 8.0×106 0.18
21.0% 20.0×106 0.16 12.0×106 0.10
21.0% 16.0×106 0.25 11.0×106 0.15
21.0% 13.0×106 0.30 8.0×106 0.18

15. FP7-ENERGY-2013-1/ n° 608396 15
List of Contents
q Introduction into the project
q Design of AVATAR Reference Wind Turbine
q Aerodynamics at high Reynolds numbers
• Airfoil measurements in pressurized DNW-HDG tunnel 1)
q Aero-elasticity of large turbines at yaw
• BEM versus free vortex wake aerodynamic modelling
19-09-16
1) Acknowledgement O. Ceyhan, O. Pires

16. FP7-ENERGY-2013-1/ n° 608396
Measurements in DNW-HDG
pressurized tunnel
• Measurements up to Re = 15M (and low M)
• DU00-W-212 selected as common airfoil
– Also measured by:
– LM up to RE=6M
– Forwind at controlled turbulent conditions
up to Re = 1M
• Results are brought into a ‘blind test’
– Measurements compared with calculations
– Blind test included participants outside project
DNW-HDG model, c=15 cm

17. FP7-ENERGY-2013-1/ n° 608396
DNW-HDG Wind Tunnel
General Tunnel Characteristics
Test section : 60cmx60cm
Fan Rpm : 200 – 820 Fan bladeangle
fixed
Tunnel Pres. : 1 – 100×105 Pa
Tunnel Temp.: ambient to 45°C

18. FP7-ENERGY-2013-1/ n° 608396
Test Section
Probe
holder for
hot wire
90 PTs at half span
Wake rake
118 pitot tubes
6 pressure taps
Kulites
4 pressure side
1 suction side
3-component
Balance
Sensicam & UV LED’s
Flow visualization

19. FP7-ENERGY-2013-1/ n° 608396
Participants/Codes
Test 1.
Re=3mil
Test 2.
Re=6mil-1
Test 3.
Re=6mil-2
Test 4.
Re=9mil-1
Test 5.
Re=9mil-2
Test 6. Test 7.
Re=12mil Re=15mil
Pt [bars] 12 34 67 34 67 67 60
Vtunnel [m/s] 25.6 19 10 28.6 15 20 28.4
Full CFD
DTU/EllipSys
Fully turbulent
Transition Yes Yes Yes Yes Yes Yes Yes
KIEL/TAU
Fully turbulent
Transition Yes Yes Yes Yes Yes Yes Yes
NTUA/Mapflow
Fully turbulent
Transition Yes Yes Yes Yes Yes Yes Yes
UoG/HMB
Fully turbulent Yes Yes
Transition Yes Yes
Forwind-IWES/OpenFOAM
Fully turbulent Yes Yes Yes Yes Yes Yes Yes
Transition
Panel
Methods
USTUTT/XFOILvUSTUTT
Fully turbulent
Transition Yes Yes Yes Yes Yes Yes Yes
ORE Catapult/XFOILv6.96
Fully turbulent
Transition Yes Yes Yes Yes Yes Yes Yes

20. FP7-ENERGY-2013-1/ n° 608396
DNW-HDG Full CFD calculations vs measurements
Effect in Blade Design parameter: Cl/Cd
-5 0 5 10 15
0
20
40
60
80
100
120
140
160
180
Alpha
Cl/Cd
Exp
DTU-Ellipsys
NTUA-MaPFlow
Kiel-TAU
F-I-OpenFOAM
UoG-HMB
Test1 Rey=3đ106
Ti3 ( 0.09% )
-5 0 5 10 15
0
20
40
60
80
100
120
140
160
180
Alpha
Cl/Cd
Exp
DTU-Ellipsys
NTUA-MaPFlow
Kiel-TAU-
F-I-OpenFOAM
UoG-HMB
Test3 Rey=6đ106
Ti3 ( 0.2% )

21. FP7-ENERGY-2013-1/ n° 608396
DNW-HDG Full CFD calculations vs measurements
Effect in Blade Design parameter: Cl/Cd
-5 0 5 10 15
0
20
40
60
80
100
120
140
160
180
Alpha
Cl/Cd
Exp
DTU-Ellipsys
NTUA-MaPFlow
Kiel-TAU
F-I-OpenFOAM
Test5 Rey=9đ106
Ti3 ( 0.24% )
-5 0 5 10 15
0
20
40
60
80
100
120
140
160
180
Alpha
Cl/Cd
Exp
DTU-Ellipsys
NTUA-MaPFlow
Kiel-TAU
F-I-OpenFOAM
Test7 Rey=15đ106
Ti3 ( 0.33% )

22. FP7-ENERGY-2013-1/ n° 608396
DNW-HDG Panel code calculations vs measurements
Effect in Blade Design parameter: Cl/Cd
-5 0 5 10 15
0
20
40
60
80
100
120
140
160
180
Alpha
Cl/Cd
Exp
ORE-XFOIL
UoS-XFOIL*
DTU-EllipSys
Test1 Rey=3đ106
Ti3 ( 0.09% )
-5 0 5 10 15
0
20
40
60
80
100
120
140
160
180
Alpha
Cl/Cd
Exp
ORE-XFOIL
UoS-XFOIL*
DTU-EllipSys
Test3 Rey=6đ106
Ti3 ( 0.2% )

23. FP7-ENERGY-2013-1/ n° 608396
DNW-HDG Panel code calculations vs measurements
Effect in Blade Design parameter: Cl/Cd
-5 0 5 10 15
0
20
40
60
80
100
120
140
160
180
Alpha
Cl/Cd
Exp
ORE-XFOIL
UoS-XFOIL*
DTU-EllipSys
Test5 Rey=9đ106
Ti3 ( 0.24% )
-5 0 5 10 15
0
20
40
60
80
100
120
140
160
180
Alpha
Cl/Cd
Exp
ORE-XFOIL
UoS-XFOIL*
DTU-EllipSys
Test7 Rey=15đ106
Ti3 ( 0.33% )

24. FP7-ENERGY-2013-1/ n° 608396
Blind test, main conclusion
– cl/cd largelydetermines the optimal aerodynamicdesign
– importance of boundarylayer transition on cl/cd has been confirmed:
– eN method performs well at all Reynolds numbers
– Correlationbased transitionmethod (state of the art in many CFD
tools!) deficient at high Reynolds numbers 1)
– New version of correlation based transitionmodel is developed with
better performance 2)
1) Niels N. Sørensen et alPrediction of airfoil performance at high Reynolds numbersEFMC 2014, Copenhagen 17-20 Sept 2014
2) S. Colonia et al Calibration of the g equation transition model for High Reynolds flows at low Mach To be published at the Science
of Matking Torque, October 2016

25. FP7-ENERGY-2013-1/ n° 608396 25
List of Contents
q Introduction into the project
q Design of AVATAR Reference Wind Turbine
q Aerodynamics at high Reynoldsnumbers
• Airfoil measurements in pressurized DNW-HDG tunnel
q Aero-elasticity of large turbines at yaw
• BEM versus free vortex wake aerodynamic modelling1)
19-09-16
1) Acknowledgement K. Boorsma, S. Voutsinas

26. ECN Aero-module
26
June 17, 2010
• ECN Aero Module: One code with aero-models of different degrees of fidelity coupled to same
structural solver (PHATAS/FOCUS)
• BEM and AWSM (Free and prescribed vortex wake model)
• Straightforward comparison of different aerodynamic models with same input
• Results are shown of azimuthal variation of induced velocity at yawed conditions:
• AWSM: Physical modelling of azimuthal variation of induced velocity at yaw
• 2 BEM implementations: Conventional Glauert model 1) and ECN developed root vortex model 2) and 3)
1) H. Glauert, A general theory for Autogyro
ARC-R-M,1111, 1926
2) J.G. Schepers An engineering model for yawed conditions,
developed on basis of wind tunnel measurements,
AIAA-99-0039 37th Aerospace Sciences Meeting and
Exhibit, Aerospace Sciences Meetings, 1999
3) J.G. Schepers ‘Engineering models in wind energy aerodynamics,’
TUDelft PhD thesis ISBN: 9789461915078, 2012

27. INNWIND.EU turbine
Results at 30 degrees yaw (30% and 95% span)
27
§ Induced velocity variation at 30% span:
• 90 degrees azimuth:
• Root vortex effects clearlyapparent in vortex wake methods (AWSM and AWSM-Prescribed)
• Conventional Glauert model for induced velocity variation deficient
• Root vortex effects predicted well by ECN-rv
§ Induced velocity variation at 30% span: Effect of root vortex at outer blade part in ECN-rv will be reduced

28. FP7-ENERGY-2013-1/ n° 608396 28
Summary
• AVATAR is an EU FP7 projects which aims to validate, improve and calibrate
aerodynamic models for 10MW+ turbines with and without flow devices and with
and without aero-elastic effects
• Several (wind tunnel) measurements have been taken which have helped to validate
and improve (sub) models relevant for 10MW+ turbines
• Models of different degrees of fidelity are evaluated on two 10 MW reference wind
turbines:
– AVATAR low induction turbine with special aerodynamic challenges
– INNWIND.EU conventional induction turbine

29. FP7-ENERGY-2013-1/ n° 608396 29
Summary
• The amount of results from the AVATAR project is far too much to present in 15-20 minutes
• AVATAR led to several model improvements and lessons learned e.g:
– Transition modelling
• Original correlation based transitionmodels deficient at high Reynolds numbers
• Updated version of correlation basedtransition models has become available
• Guidelines on the employment of transition (and turbulence) models formulated
– Improved predictions for low Mach conditions in compressible codes
– Improved models for thick airfoils
– Improved models for flow devices (flaps, vortex generators, root spoilers)
– First possibilities for rotor model improvements identified (many more will follow…)
– Improved calculational efficiency and reduced time to set-up calculation
– Expansion/integration of codes (e.g. coupling of aero-elastic models to free vortex wake methods)
– Best practice guidelines on grid resolutions and temporal resolution
• Need for vortex corrections at some grid topologies with limited domain size
– Calibration of engineering methods from CFD not straightforward
• Techniques are developed and tested to derive lifting line variables from CFD
– Many more improvements and lessons learned will follow!

30. FP7-ENERGY-2013-1/ n° 608396 30
Dissemination of results
– All technical deliverables are public:
http://www.eera-avatar.eu/publications-results-and-links/
– Web based validation platform is under development
(http://windbench.net/avatar)
– AVATAR session at IRPWIND-EERA Joint Wind R&D conference,
September 19, Amsterdam, the Netherlands
– Introduction (Gerard Schepers, ECN)
– Advanced Aerodynamic Modelling (Niels Sørensen, DTU)
– Flow device aerodynamics (Alvaro Gonzalez, CENER)
– Roadmap for further engineering modelling improvements (Gerard Schepers, ECN)
– AVATAR session at Science of Making Torque, October 7, Munich Germany
– 5 Oral presentations
– Latest results from the EU project AVATAR: Aerodynamic modelling of 10 MW wind turbines (Gerard Schepers (ECN) et al)
– CFD code comparison for 2D airfoil flows (Niels Sørensen (DTU) et al)
– Experimental benchmark and code validation for airfoils equipped with passive vortex generators (Daniel Baldacchino (TUDelft) et al)
– Computing the flow past Vortex Generators: Comparison between RANS Simulations and Experiments (M. Manolesos (NTUA) et al)
– Results of the AVATAR project for the validation of 2D aerodynamic models with experimental data of the DU95W180 airfoil with unsteady flap (Carlos Fereira (TUDelft) et al)
– Introduction to 7 posters

31. Consortium
FP7-ENERGY-2013-1/ n° 608396
Coordinator:
Partners in alphabetical order:

32. This project has received funding from the European Union’s Seventh Programme for research, technological development and
demonstration under grand agreement No FP7-ENERGY-2013-1/n° 608396 .
Thank you for your attention