Structural design of spars for 100-m biplane wind turbine blades

Transcription

1 Structural design of spars for 100-m biplane wind turbine blades Perry M. Johnson & Richard E. Wirz Wirz Research Group, Energy Innovation Laboratory Department of Mechanical and Aerospace Engineering University of California, Los Angeles AWEA Windpower 2012 Atlanta, GA June 5, 2012 Funding provided by UCLA Eugene V. Cota-Robles Fellowship California Energy Commission Energy Innovations Small Grant

2 Overview Why modify inboard region? Potential of the biplane Structural advantages Aerodynamic advantages Design & parametric analysis Why analyze spars? Initial results Conclusions & Outlook Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

3 Previous approaches Blades must support large bending loads Larger turbines Longer blades Larger bending loads Source: Hau & von Renouard, Wind Turbines, 2nd ed., The structural design of the inboard region is driven by these loads. flatback airfoils Jackson et al., Innovative Design Approaches for Large Wind Turbine Blades, Wind Energy, Is there a better design for the inboard region? Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

4 Biplane blades could improve the performance of the inboard region New approach: biplane inboard region* Artistic rendering, courtesy of Phillip Chiu Potential structural benefits Stiffer, lighter blades Higher cut-out wind speeds Potential aerodynamic benefits More torque, less drag These benefits are likely significant Lower cut-in wind for large (3-7 MW) and ultra-large speeds (8-10 MW) turbines * Wirz, U.S. Provisional Application 61/308,214, Wirz and Johnson, 29 th AIAA Applied Aero. Conf., Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

5 Structural advantage of biplanes a stiffer inboard region biplane airfoils form flanges similar to an I-beam to efficiently support loads Source: Wirz and Johnson, Aero-structural Performance of Multiplane Wind Turbine Blade, 29 th AIAA Applied Aero. Conf., Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

6 Aerodynamic advantage of biplanes a more slender inboard region biplane thick monoplane Improved: L/D C L,max stall behavior Why did biplanes disappear? Seemed to be a high drag configuration* * R. Addoms, Aerodynamic and structural design considerations for high lift biplane wing systems, Ph.D. Thesis, UCLA, biplane Sopwith Camel (1917) Jetplanes.co.uk struts Phillip Chiu, Aerodynamic Performance of Biplane Airfoils for Wind Turbine Blades, AWEA Windpower, June 4, bracing wires Ragheb and Selig, Multi-Element Airfoil Configurations for Wind Turbines, 29th AIAA Applied Aero. Conf., Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

7 A new design method is needed for the radical design of the biplane blade How to include a biplane into overall blade structure? joint length, r j =? gap, g =? Conventional approach for monoplane blade Inside-out approach for biplane blade 1. Design airfoils for aerodynamic exterior 2. Fit spar structure inside airfoils 1. Design internal spar structure 2. Fit airfoil exterior over spar Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

8 deflection Objectives 1. Design spars for biplane blade research 2. Use simple load cases to compare the structural performance of different biplane spars 3. Identify the effect of design parameters on the structural performance of biplane spars joint length, r j =? gap, g =?? span Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

9 Inside-out approach analyze spars 100-m Sandia research blade* monoplane spar * Griffith and Ashwill, The Sandia 100-meter All-glass Baseline Wind Turbine Blade: SNL100-00, (figure not to scale) spar geometry composite layup materials biplane blade joint length, r j =? biplane spars gap, g =? note: cylindrical root neglected in this analysis Johnson and Wirz, High-Strength Wind Turbine Blades and Wings, UCLA Invention Report, Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

10 box-beam Inside-out approach assume spar is representative of entire blade Spar is the primary load-bearing component in the blade*, Primary load-carrying fibers spar caps Shear webs stabilize the spar caps under shear forces Closed box section can withstand torsional loads Airfoil shells are not load-bearing Spar is defined to include: 2 principal shear webs 2 spar caps Root buildup adjacent to box-beam (figure not to scale) * Lowe and Satterly, Comparison of Coupon and Spar Tests, Design of composite structures against fatigue: applications to wind turbine blades, D. Bannister, Materials technology for the wind energy market, JEC Magazine, Peery & Azar, Aircraft Structures, Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

11 box-beam Inside-out approach assume spar is representative of entire blade Spar is the primary load-bearing component in the blade*, Primary load-carrying fibers spar caps Shear webs stabilize the spar caps under shear forces Closed box section can withstand torsional loads Airfoil shells are not load-bearing Spar is defined to include: 2 principal shear webs 2 spar caps Root buildup adjacent to box-beam Assumptions Assume rectangular cross-section Neglect twist (figure not to scale) * Lowe and Satterly, Comparison of Coupon and Spar Tests, Design of composite structures against fatigue: applications to wind turbine blades, D. Bannister, Materials technology for the wind energy market, JEC Magazine, Peery & Azar, Aircraft Structures, Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

12 Design & analysis of the monoplane spar Sandia research blade* - geometry, layup, materials define cross-sectional design parameters - cross-sectional mesh (TrueGrid) - 2D FEM cross-sectional analysis (VABS) - compute 6x6 stiffness matrices monoplane spar - neglect everything except spar components * D. T. Griffith and T. D. Ashwill, The Sandia 100-meter All-glass Baseline Wind Turbine Blade: SNL100-00, postprocessing - deflections - bending moments - (stresses/strains) load case simulation (DYMORE) define geometrically exact 1D beam model (DYMORE) - 3 rd -order beam elements - 6 DOF per node Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

13 Design & analysis of the biplane spar monoplane spar - geometry, layup, materials (derived from Sandia blade) define cross-sectional design parameters - cross-sectional mesh (TrueGrid) - 2D FEM cross-sectional analysis (VABS) - compute 6x6 stiffness matrices biplane spar - replace inboard region with biplane postprocessing - deflections - bending moments - (stresses/strains) load case simulation - define equivalent load for biplane region define geometrically exact 1D beam model (DYMORE) - 3 rd -order beam elements - 6 DOF per node - define joint length and gap repeat for parametric analysis Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

14 Monoplane spar and biplane spars for 100-m blades monoplane spar 5.3 m biplane spars (15 configurations) Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

15 All cross-sections had equal areas so all spars had the same mass per unit span Laminate dimensions and material properties were based on 100-m Sandia research blade* * D. T. Griffith and T. D. Ashwill, The Sandia 100-meter All-glass Baseline Wind Turbine Blade: SNL100-00, Albuquerque, NM, (figure not to scale) Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

16 All cross-sections had equal areas so all spars had the same mass per unit span Biplane cross-sections (half-height) Biplane cross-sections (full-height) Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

17 Parametric analysis needs fast and accurate design tools Direct approach 3D finite element analysis (FEA) High accuracy Time consuming Model setup Computational time Not fast enough for parametric analysis Alternate approach 1D FEA & 2D cross-sectional analysis DYMORE* & VABS, Fast 2-3 orders less computing time, Accurate (c.f. 3D FEA, ) Modeled wind turbine blades * Bauchau, Multibody System Dynamics, Hodges & Yu, Wind Energy, Chen, Yu, & Capellaro, Wind Energy, Otero & Ponta, J. Solar Energy Eng,, Source: Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

18 Numerical methods monoplane spar 1D beam meshes biplane spar 3 rd -order beam elements (mid-element nodes not shown) monoplane spar static load distributions biplane spar Max load magnitude: F 0 = 1000 N/m Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

19 Some structural characteristics are improved with the biplane spar: smaller deflections and bending moments biplane spar design parameters: r j /R = g/c = 1.25 Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

20 Deflections and bending moments decrease as joint length increases (up to a point) (lighter colors are better) Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,

21 Conclusions & Outlook smaller tip deflections smaller bending moments Designed biplane spars Some structural characteristics are improved Smaller tip deflections Smaller bending moments near root Cross-section height and joint length have a strong influence on structural performance 3D FEA is needed for future studies More load cases are necessary, but results suggest that weight reductions may be possible Manufacture of joint will be challenging Ultimate goal: design biplane blade with airfoils, perform direct comparison to Sandia blade Aeroelastic simulations Fatigue and buckling analyses Johnson & Wirz, Structural design of spars for 100-m biplane wind turbine blades, June 5,