Offshore Wind RD&D: Large Offshore Rotor Development
Sandia National Laboratories Wind Energy Technologies Department, creates and evaluates innovative large blade concepts for horizontal axis wind turbines to promote designs that are more efficient aerodynamically, structurally, and economically. Recent work has focused on the development of a 100-meter blade for a 13.2 MW horizontal axis wind turbine, a blade which is significantly longer than the largest commercial blades that existed at the beginning of this project (approximately 60 meters long). The table provides a summary of four design studies that were performed for 100-meter blades:
All-glass Baseline Blade:
114 ton weight
Carbon Design Studies:
74 ton weight
Advanced Core Material:
59 ton weight
49 ton weight
Detailed design models (Sandia NuMAD format) for each of the four blade designs can be downloaded below. A 13.2 MW turbine model (NREL FAST format) is also available for download.
Initial All-Glass 100-m Blade Studies: SNL100-00
The initial study focused on development, documentation, and dissemination of the Sandia 100-m All-glass Baseline Wind Turbine Blade, termed “SNL100-00”, which employs conventional architecture and fiberglass-only composite materials (Reference 1). A detailed composite layup and geometry are available through the links below, along with the associated 13.2 MW Turbine Design Models.
Design loads analysis of the baseline model based on a critical subset of international standards demonstrated acceptance of the design with respect to strength, fatigue, deflection, and buckling. Challenges and opportunities for large blade research are summarized below in the referenced reports and linked documents.
These 100-meter blade models can provide a starting point for consideration of blade innovations by the research community with potential performance improvement, weight reduction, and cost improvements. A design scorecard is provided below for use by researchers to compare the effect of innovations on the principal design drivers which include weight, fatigue life, buckling, tip deflection, maximum strains, and aeroelastic stability (flutter margin). The 13.2 MW turbine models also provide a starting point for turbine and turbine control studies.
Aeroelastic stability (flutter) and aeroelastic performance of large blades were discussed in References 2, 4, and 5.
100-m Carbon Blade Design Studies: SNL100-01
An updated 100-m blade reference model was developed, termed as SNL100-01 (references 6-9). The new design was a modification to the baseline SNL100-00 design with the same external geometry; however, a carbon spar cap was introduced into the design. The weight of the SNL100-01 design is about 74,000 kg, which is a 35% reduction in weight from the baseline all-glass blade. A series of carbon spar cap designs were analyzed and documented with SNL100-01 as the final design model. In addition to the new spar cap, additional associated modifications were made including reduction in spar and TE reinforcement width, movement of the two principal spar caps, and thinning of the root.
References 10 and 11 describe the SNL Blade Manufacturing Cost Model (version 1.0) that was developed under this project.
SNL100-02: Advanced Core Material and New Core Strategy
New core materials were evaluated to produce the SNL100-02 design (Reference 12). Various foams, balsa, and structured (engineered) core identified in an industry survey of core materials, were evaluated along with a new core material strategy in a series of structural design studies. The new strategy utilized balsa in critical buckling areas (Trailing Edge Panel: Inboard) and PET foam in the non-critical buckling areas (Trailing Edge Panel: Outboard), as shown in the figure. In addition to the weight reduction achieved, a secondary benefit was found in that these core materials are regrowable (in the case of balsa) and recyclable (in the case of PET foam).
SNL100-03: Flatback Airfoils and Blade Slenderness Study
The effects of flatback airfoils were evaluated in a fourth and final series of design studies. The advantages and disadvantages of high blade slenderness low blade solidity were quantified with respect to tip deflection, flap-wise & edge-wise fatigue resistance, panel buckling capacity, flutter speed, manufacturing labor content, blade total weight, and aerodynamic design load magnitude (References 13 and 14).
Challenges and Opportunities
A 100-m blade using conventional geometry and all-glass materials is possible. All design requirements are satisfied including maximum strains, tip-tower clearance, buckling resistance, and fatigue life. However, the blade weight for the initial SNL100-00 design was very high (and not cost-effective). The subsequent SNL100-01, SNL100-02, and SNL100-03 blade studies demonstrated a pathway for weight reduction, as shown in the figure where projections of weight growth are compared with commercial blades and research concept blades (including the SNL100-XX series).
Current and Future Work: Potential Research Directions
Significant opportunity exists to reduce weight and cost through innovations and structural optimization. These reference models provide a starting point for block and turbine design and analysis studies. In design studies, carbon fiber, very thick airfoils such as flatback airfoils, bend-twist coupling, geometric sweep, pre-bending, and unique architecture, anti-buckling devices, structured core, and active control could be considered. Many of these approaches have been explored in these SNL100-XX design studies.
Other considerations for future work and potential research in large rotor technology are outlined in the SNL100-00 design report (Reference 1) provided below, Reference 7, and the project final design report for SNL100-03 (Reference 14).
Sandia Blade and Turbine Design Models: Reports and Model Files
13.2MW land-based turbine with SNL100-01 or SNL100-02 Blades
Refer to “SNL13.2MW-00-Land” Turbine and “SNL100-01” or “SNL100-02” Blade Downloads
13.2 MW land-based turbine with SNL100-03 Blades
Refer to “SNL13.2MW-00-Land” Turbine and “SNL100-03” Blade Downloads
13.2 MW turbine on offshore foundation
Potential future release
Griffith, D.T. and Ashwill, T.D., “The Sandia 100-meter All-glass Baseline Wind Turbine Blade: SNL100-00,” Sandia National Laboratories Technical Report, SAND2011-3779, June 2011 (1.22MB PDF).
Resor, B.R., Owens, B.C., and Griffith, D.T., “Aeroelastic Instability of Very Large Wind Turbine Blades,” Proceedings of the European Wind Energy Conference Annual Event (Technical Track Paper/Poster), April 16-19, 2012, Copenhagen, Denmark.
Griffith, D.T. and Ashwill, T.D., and Resor, B.R., “Large Offshore Rotor Development: Design and Analysis of the Sandia 100-meter Wind Turbine Blade,” 53rd AIAA Structures, Structural Dynamics, and Materials Conference, Honolulu, HI, April 23-26, 2012, AIAA2012-1499 (1.21MB PDF).
Corson, D., Griffith, D.T., et al, “Investigating Aeroelastic Performance of Multi-MegaWatt Wind Turbine Rotors Using CFD,” AIAA Structures, 53rd Structural Dynamics and Materials Conference, Honolulu, HI, April 23-26, 2012, AIAA2012-1827 (1.46MB PDF).
Owens, B.C., Griffith, D.T., Resor, B.R., and Hurtado, J.E., “Impact of Modeling Approach on Flutter Predictions for Very Large Wind Turbine Blade Designs,” Proceedings of the American Helicopter Society (AHS) 69th Annual Forum, May 21-23, 2013, Phoenix, AZ, USA, Paper No. 386.
SNL100-01 Carbon Design Studies:
Griffith, D.T., “The SNL100-01 Blade: Carbon Design Studies for the Sandia 100-meter Blade,” Sandia National Laboratories Technical Report, SAND2013-1178, February 2013 (1.25MB PDF).
Griffith, D.T., Resor, B.R., Ashwill, T.D., “Challenges and Opportunities in Large Offshore Rotor Development: Sandia 100-meter Blade Research,” AWEA WINDPOWER 2012 Conference and Exhibition, Scientific Track Paper, Atlanta, GA, USA, June 3-6, 2012 (560KB PDF).
Griffith, D.T. and Johanns, W., “Carbon Design Studies for Large Blades: Performance and Cost Tradeoffs for the Sandia 100-meter Wind Turbine Blade,” 54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, April 8-11, 2013, Boston, MA, USA, AIAA-2013-1554.
Sandia Blade Manufacturing Cost Model (version 1.0):
Griffith, D.T. and Johanns, W., “Large Blade Manufacturing Cost Studies Using the Sandia Blade Manufacturing Cost Tool and Sandia 100-meter Blades,” Sandia National Laboratories Technical Report, April 2013, SAND2013-2734.
Johanns, W. and Griffith, D.T., “User Manual for Sandia Blade Manufacturing Cost Tool: Version 1.0,” Sandia National Laboratories Technical Report, April 2013, SAND2013-2733.
SNL100-02 Advanced Core Strategy Design Studies:
Griffith, D.T., “The SNL100-02 Blade: Advanced Core Material Design Studies for the Sandia 100-meter Blade,” Sandia National Laboratories Technical Report, November 2013, SAND2013-10162.
SNL100-03 Flatback Airfoil Design Studies:
Griffith, D.T. and Richards, P.W., “Investigating the Effects of Flatback Airfoils and Blade Slenderness on the Design of Large Wind Turbine Blades,” Proceedings of the European Wind Energy Association (EWEA) Annual Event, March 2014, Barcelona, Spain, PO 225.
Griffith, D.T., and Richards, P.W., “The SNL100-03 Blade: Design Studies with Flatback Airfoils for the Sandia 100-meter Blade,” Sandia National Laboratories Technical Report, September 2014, SAND2014-18129.
Additional Documentation for Blade and Turbine Model Files:
“Sandia Large Rotor Design Scorecard,” Sandia National Laboratories Technical Report, SAND2011-9113P, December 2011 (182KB PDF).
Griffith, D.T., Resor, B.R., “Description of Model Data for SNL13.2-00-Land: A 13.2 MW Land-based Turbine Model with SNL100-00 Blades,” Sandia National Laboratories Technical Report, SAND2011-9310P.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.