NREL 5MW Rotor Geometry

Discuss the theory and modeling of rotor aerodynamics.

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Kisorthman.Vimalakanthan
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NREL 5MW Rotor Geometry

Hi Guys,

Firstly I would like to say I'm privileged to have access to the forum. I'm a PhD student. My research is focused on aerodynamics of wind turbine, At the moment I'm trying to build CAD model of the NREL 5MW baseline rotor so I can make a GRID and undertake a CFD analysis, but having some difficulties with the geometric definition that are available regarding the NREL 5MW rotor. I’ll give a summary what I have gathered so far.

The geometry of the NREL 5MW blade is based on the LMH64-H blade (reduced rotor and hub diameter) [1], which was initially used on the DOWEC 6MW rotor. Unfortunately I have been unsuccessful in obtaining the geometric definition of LMH64-5 blade, except the DOWEC paper [2]. In the NREL 5MW document the airfoils are given are in an abbreviated form, but using the DOWEC document [2], the airfoil names used on the LMH64-5 blade can be obtained with some confusions. Here is what I have decrypted from comparing NREL[1] and DOWEC[2] publications.

DU40_17 = DU 99 W 405 LM
DU35_A17 = DU 99 W 350
DU30_A17 = DU 97 W 300 LM
DU25_A17 = DU 91 W2-250
DU21_A17 = DU 93-W-210 LM
NACA64_A17 = NACA 64-618

Is this Correct?

LM indicates original blade with a reduced trailing edge thickness i.e. DU 99 W 405 LM is the DU 99 W 405 airfoil with smaller trailing edge thickness. ‘_A17’ indicate that the blade section has an aspect ratio of 17.

TU Delft have informed me that all the airfoils used in the LMH64-5 DOWEC blade are 'probably' the LM profiles. There is also another uncertainty that arises in the airfoil sections, the DU airfoils particularly DU 99 W 405 LM & DU 99 W 350 LM has an adjusted form(see atached image). Hence I'm not entirely sure which airfoil section the NREL have used for their 5MW baseline rotor.

Lastly from the NREL document [1], I was able to obtain the axial position on the airfoil section where the pitch axis passes through (AeroCent-0.25). But the information regarding the tangential position on the airfoil, where the pitch axis passes through is not available especially that fact that LMH64-5 is a prebend blade, therefore this information is vital to create an accurate geometry of the blade.

Could anyone please help to with my question regarding the exact airfoil sections used and how they are stacked along the NREL 5MW rotor blade?
Any help is greatly appreciated.

P.S. I have written a lot because i thought it will help others who may be doing something similar to me, hope this is ok.

Reference
1. H Jonkman J, Butterfield S, Musial W, Scott G. Definition of a 5-MW reference wind turbine for offshore system
development. Technical Report NREL/TP-500-38060, National Renewable Energy Laboratory, Golden, CO, 2009.

2. Kooijman, H. J. T., Lindenburg, C., Winkelaar, D., and van der Hooft, E. L., “DOWEC 6 MW Pre-Design: Aero-elastic modeling of the DOWEC 6 MW pre-design in PHATAS,” DOWEC Dutch Offshore Wind Energy Converter 1997–2003 Public Reports [CD-ROM], DOWEC 10046_009, ECN-CX--01-135, Petten, the Netherlands: Energy Research Center of the Netherlands, September 2003..J.T.
Attachments
Comparison of Adjusted an Original LM airfoils
Adjusted2.JPG (8.8 KiB) Viewed 35625 times
Kisorthman Vimalakanthan MEng PhD
Dept. of Power and Propulsion
School of Engineering
Cranfield University
Cranfield
Bedford, MK43 0AL
UK.
Email: k.vimalakanthan@gmail.com

Marshall.Buhl
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Re: NREL 5MW Rotor Geometry

Kishore,

Maybe Jason, who made up the NREL 5MW fantasy turbine should answer, but I'll try to help now.

As far as I know, the design of the turbine never included such details. Jason just came up with a twist, chord, and sufficient aerodynamic data to be used by non-CFD codes. This turbine has been used in the IEC Annex XXIII OC3 code comparison, and I am not aware of any of the programs in the comparison being CFD-based. Details of the shape of blades is very proprietary and I doubt any companies would be willing to give them to you.

I know a lot of CFD codes use NREL's Phase VI Unsteady Aerodynamics Experiment (UAE) turbine for testing their codes because such data are available. We designed the blade just for this test and then tested the 10m turbine in a gigantic wind tunnel. The test data could be made available for validating your model. Nothing about the turbine is protected intellectual property. Unless you really need to model a large turbine, I'd recommend you model the UAE turbine using your CFD code.

Good luck!

Marshall
Mr. Marshall L. Buhl Jr.
NWTC-3811
National Renewable Energy Laboratory
Golden, CO 80401 USA
Marshall.Buhl@nrel.gov
Voice: +1 (303) 384-6914
Cell: +1 (303) 915-6623
Fax: +1 (303) 384-7079

Jason.Jonkman
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Re: NREL 5MW Rotor Geometry

Dear Kishore,

Your understanding of the airfoil names of the NREL 5-MW baseline wind turbine is correct. Marshall is also correct in that the NREL 5-MW specifications report ([1]) was never meant to include enough detail to develop a CAD model or CFD mesh.

That said, the NREL 5-MW turbine has been used around the world for many conceptual design and analysis studies--including being adopted as the reference turbine in the EU UpWind research program, the IEA Wind Task 23 OC3 project, and the IEA Wind Task 30 OC4 project. Due to its widespread use, there have been several groups who have developed CAD models and CFD meshes of this turbine. Each one has had to take a number of liberties when they defined the external shape of the blade (and other turbine components) needed to create such a model. Examples of groups who have developed CFD meshes of the NREL 5-MW turbine include the University of California-Davis, the University of California-San Diego, and Risø DTU of Denmark. I also know that the University of Maine has also developed a CAD model of the the NREL 5-MW blade. I suggest you contact one of the developers of these models to see what liberties they took in their model development.

The true LMH64-5 blade has built-in prebend to increase tower clearance. However, as stated in [1], the NREL 5-MW baseline turbine simplifies the blade by replacing the prebend with a 2.5 deg upwind blade precone.

The definition of AeroCent has been confusing to many and we plan to change the FAST inputs to remedy this. Until then, please note that AeroCent in FAST is used to locate the reference point relative to the pitch axis for which aerodynamic (lift, drag, pitching) coefficients are defined. AeroCent in FAST is defined as follows:

AeroCent = 0.25 - [ (fraction of chord from leading edge to actual pitch axis) - (fraction of chord from leading edge to aerodynamic coefficient reference point) ]

(The 0.25 in the equation above comes from FAST’s assumption that the pitch axis passes through 25% chord.)

We plan to update FAST by replacing input AeroCent with two new inputs as follows:

PitchAxis = Fraction of chord from leading edge to pitch axis
AeroRef = Fraction of chord from leading edge to aerodynamic coefficient reference point

Thus:

AeroCent = 0.25 - [ PitchAxis - AeroRef ]

I never actual specified the values of PitchAxis or AeroRef in the specifications report for the NREL 5-MW wind turbine. However, for your reference, the values are as follows:

Radius BlFract PitchAxis AeroRef
(m) (-) (-) (-)
1.50 0.00000 0.50000 0.50000
1.70 0.00325 0.50000 0.50000
2.70 0.01951 0.49951 0.49902
3.70 0.03577 0.49510 0.49020
4.70 0.05203 0.48284 0.46569
5.70 0.06829 0.47059 0.44118
6.70 0.08455 0.45833 0.41667
7.70 0.10081 0.44608 0.39216
8.70 0.11707 0.43382 0.36765
9.70 0.13335 0.42156 0.34311
10.70 0.14959 0.40931 0.31863
11.70 0.16585 0.39706 0.29412
12.70 0.18211 0.38481 0.26962
13.70 0.19837 0.37500 0.25000
14.70 0.21465 0.37500 0.25000
15.70 0.23089 0.37500 0.25000
16.70 0.24715 0.37500 0.25000
17.70 0.26341 0.37500 0.25000
19.70 0.29595 0.37500 0.25000
21.70 0.32846 0.37500 0.25000
23.70 0.36098 0.37500 0.25000
25.70 0.39350 0.37500 0.25000
27.70 0.42602 0.37500 0.25000
29.70 0.45855 0.37500 0.25000
31.70 0.49106 0.37500 0.25000
33.70 0.52358 0.37500 0.25000
35.70 0.55610 0.37500 0.25000
37.70 0.58862 0.37500 0.25000
39.70 0.62115 0.37500 0.25000
41.70 0.65366 0.37500 0.25000
43.70 0.68618 0.37500 0.25000
45.70 0.71870 0.37500 0.25000
47.70 0.75122 0.37500 0.25000
49.70 0.78376 0.37500 0.25000
51.70 0.81626 0.37500 0.25000
53.70 0.84878 0.37500 0.25000
55.70 0.88130 0.37500 0.25000
56.70 0.89756 0.37500 0.25000
57.70 0.91382 0.37500 0.25000
58.70 0.93008 0.37500 0.25000
59.20 0.93821 0.37500 0.25000
59.70 0.94636 0.37500 0.25000
60.20 0.95447 0.37500 0.25000
60.70 0.96260 0.37500 0.25000
61.20 0.97073 0.37500 0.25000
61.70 0.97886 0.37500 0.25000
62.20 0.98699 0.37500 0.25000
62.70 0.99512 0.37500 0.25000
63.00 1.00000 0.37500 0.25000

You should be able to match the AeroCent data provided in the specifications report with the PitchRef and AeroRef data above.

I hope that helps.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Kisorthman.Vimalakanthan
Posts: 11
Joined: Thu Jan 27, 2011 1:36 pm
Organization: Cranfield, ECN
Location: Netherlands/UK

Re: NREL 5MW Rotor Geometry

Thanks a lot for these information guys. Jason I am aware of the analysis on NREL 5MW rotor by the combined effort of the University of California and the University of rise*. I have tried to contact them regarding the stacking and airfoil information, unfortunately no response from them. But I was not aware that the University of Maine conducting studies on the NREL baseline turbine, so I will contact them just as you have suggested.

Could you please confirm if

DU35_A17 = DU 99 W 350 or DU 99 W 350 LM?
DU25_A17 = DU 91 W2-250 or DU 91 W2-250 LM?
Aerodynamic coefficient reference point = Aerodynamic center or Center of pressure?

In your development of the NREL 5MW turbine, was any of the airfoil section used in the NREL 5MW rotor blade was an 'adjusted' DU airfoil?

In terms of liberties you say Jason, where would you suggest the tangential position of the pitch axis be placed on each of the airfoil sections, for the NREL 5MW rotor blade? I.e. Camber line, Chord line or at a specific point (see attached image).

Your help is greatly appreciated guys.

*Bazilevs, Y., Hsu, M. -., Akkerman, I., Wright, S., Takizawa, K., Henicke, B., Spielman, T. and Tezduyar, T. E. (2011), "3D simulation of wind turbine rotors at full scale. Part I: Geometry modeling and aerodynamics", International Journal for Numerical Methods in Fluids, vol. 65, no. 1-3, pp. 207-235.

Thank you,
Kind regards,
Kishore
Attachments
Tangential position (recreated from ref[*])
Tangential.jpg (37.86 KiB) Viewed 35590 times
Kisorthman Vimalakanthan MEng PhD
Dept. of Power and Propulsion
School of Engineering
Cranfield University
Cranfield
Bedford, MK43 0AL
UK.
Email: k.vimalakanthan@gmail.com

Jason.Jonkman
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Re: NREL 5MW Rotor Geometry

Dear Kishore,

I can't answer your question on the DU airfoils. The specifications of the NREL 5-MW turbine don't go into this detail. I suggest you contact the authors of Ref. [1] for clarification.

The center of pressure is the point in the airfoil where the aerodynamic moment is zero. However, this location is not very useful because the location moves with angle of attack. The aerodynamc center is the point in the airfoil where the aerodynamic moment does not change with lift coefficent. However, this only occurs at small angles of attack. Instead, airfoil coefficients can all be expressed relative to a fixed location in the airfoil if one includes pitching moment data in addition to drag and lift—it is this fixed location that we refer to as the aerodynamic center in FAST. That is, the aerodynamic center in FAST is simply the reference location in the airfoil about which the lift, drag, and pitching moment coefficients are defined.

The pitch axis in the NREL 5-MW turbine is assumed to pass through the chordline of each airfoil.

I hope that helps.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Kisorthman.Vimalakanthan
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Joined: Thu Jan 27, 2011 1:36 pm
Organization: Cranfield, ECN
Location: Netherlands/UK

Re: NREL 5MW Rotor Geometry

Thanks Jason for your swift responce. The pitch axis information was the main priority, im really glad that you have solved that for me. I have tried contacting the guys at DOWEC but once agin no responce from them, maybe I will contact them again.

Kind Regards,
Kishore
Kisorthman Vimalakanthan MEng PhD
Dept. of Power and Propulsion
School of Engineering
Cranfield University
Cranfield
Bedford, MK43 0AL
UK.
Email: k.vimalakanthan@gmail.com

Anja.Grant
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Joined: Wed Aug 03, 2011 8:09 am
Organization: NTNU
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Re: NREL 5MW Rotor Geometry

Dear Jason,

I know this thread is a couple of months old now, I would just like to ask a related question if that's ok. I am currently working as part of a research group at NTNU to develop software for aeroelastic analysis of the NREL 5MW reference turbine. We are interested in the location of the blade pitch axis for the visualisation in the software. After reading the values above that you have listed for the blade pitch axis, I am interested to know why is it that the blade pitch axis is not located at the centre of all of the cylindrical airfoil sections, so for a radius up to 9.7m?

Thank you in advance.
Kind regards,

Anja

Jason.Jonkman
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Re: NREL 5MW Rotor Geometry

Dear Anja,

The root of the NREL 5-MW blade remains cylindrical only for a few meters; it then transitions to an airfoil shape. In the NREL 5-MW specifications report, the aerodynamics of the stations that are transitioning to an airfoil shape are approximated with drag-only airfoil data. While these innermost airfoil data tables are named "Cylinder1.dat" and "Cylinder2.dat", this doesn't mean that all stations are pure cylinders.

I hope that clarifies things.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Anja.Grant
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Organization: NTNU
Location: Norway

Re: NREL 5MW Rotor Geometry

Dear Jason,

Thank you for the reply. That's all clear now.

Kind regards,

Anja

Jason.Jonkman
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Re: NREL 5MW Rotor Geometry

Dear all,

Nando Timmer of TU Delft has graciously allowed us to publish the airfoil coordinates of the DU airfoils used by the NREL 5-MW wind turbine / DOWEC blade. Please see the spreadsheet attached.

The spreadsheet also contains the original 2D airfoil-data coefficients (without corrections for 3D effects, such as rotational stall delay).

Best regards,
Attachments
DOWEC-NREL 5MW blade airfoil data-v2.xls
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Matias.Sessarego
Posts: 4
Joined: Fri Feb 17, 2012 9:50 pm
Organization: University of Calgary

Re: NREL 5MW Rotor Geometry

Hi everyone,

Does anyone have the thickness/chord (t/c) distribution of the NREL 5MW blade? Figure 7 in the DOWEC report displays this information and I can digitize it, but it would be better to have the exact numbers.

DOWEC 6 MWPRE-DESIGN
Aero-elastic modelling of the DOWEC 6 MWpre-design in PHATAS
DOWEC-F1W2-HJK-01-046/9
public version
H.J.T. Kooijman
C. Lindenburg
D. Winkelaar
E.L. van der Hooft

I am also having trouble understanding Table 1 in this paper. Does the "modelled from rotor span distance (input)" pertain to the "relative thickness" or the "modelled from blade thickness"?

Jason.Jonkman
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Re: NREL 5MW Rotor Geometry

Dear Matias,

The airfoil thicknesses can be derived from the airfoil names. For example, "DU21" is an airfoil with t/c of 21%. This interpretation is consistent with Table 1 from the reference you've idenified.

My interpretation of Table 1 from that reference is that the "modeled from rotor span distance (input)" is the distance along the blade from the axis of rotation about which a given airfoil is modeled until the next row (a stepwise representation). For example, "Cylinder 1" is modeled from 1.80 to 5.98 m along the blade, "Cylinder 2" is modeled from 5.98 m to 10.15 m along the blade, etc.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Matias.Sessarego
Posts: 4
Joined: Fri Feb 17, 2012 9:50 pm
Organization: University of Calgary

Re: NREL 5MW Rotor Geometry

Hi Jason,

Thanks for your reply. The reason why I am asking this is because I want to interpolate airfoil data/profiles much like in HARP_Opt (see page 6-7 http://wind.nrel.gov/designcodes/simula ... RP_Opt.pdf). In order to do this I need a continuous (t/c) distribution from root to tip of the NREL blade like on Table 3.3 on page 50 of this thesis (https://library.umaine.edu/theses/pdf/MartinH2011.pdf). I think the author of this thesis obtained the documented part of this distribution from Timmer but I'm not sure. I would like to obtain the distribution from an original source if possible. Otherwise, I will probably just use the distribution given in this thesis.

Thanks,

Matias

Dawn.Ward
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Re: NREL 5MW Rotor Geometry

Dear Jason,

Within the technical report you wrote called ‘Dynamics Modeling and Loads Analysis of an Offshore Floating Wind Turbine’ published in 2007, which utilizes the NREl 5MW turbine, you state that for the pitch to stall analysis you smoothed the airfoil-data coefficients near stall to eliminate the existing fluctuations that could have led to numerical problems in the BEM aerodynamic-induction solution algorithm. You did this by modified the airfoils by manually manipulating the lift coefficients.

Would it be possible to get the values of the changes you made?

Also has any further work been done on a stall operated blade for the NREL 5MW turbine, or are there airfoils that you could recommend for the NREL 5MW turbine operating in active pitch to stall control?

Thanks,
Dawn

Jason.Jonkman
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Re: NREL 5MW Rotor Geometry

Dear Dawn,

I've attached the manually smoothed airfoil data that is mentioned in that report.

NREL has not done any further work on active stall regulation of the NREL 5-MW turbine. Sorry, but I'm not sure I have any specific recommendations.

Best regards,
Attachments
Smoothed.zip
Manually Smoothed Airfoil Data
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov