Sandia 2014 Wind Turbine Blade Workshop- Loth
Download as PPT, PDF0 likes7,471 views
The document discusses potential benefits of downwind force-aligned rotors for extreme-scale offshore wind turbines. It describes how load alignment through concepts like morphing blades and pre-aligned blade segments could help reduce structural loads and mass. Steady-state analysis shows morphing could allow major reductions in blade and tower mass. Pre-alignment offers load savings with less complexity than morphing. Aerodynamic shrouds around the tower also help reduce wake effects. More analysis is still needed to determine the feasibility and benefits of these force-aligned downwind concepts.
Sandia 2014 Wind Turbine Blade Workshop- Loth
- 1. Downwind Force-Aligned Rotors for Extreme-Scale Off-Shore Wind 1 Eric Loth University of Virginia
- 2. 2 Early evaluations of new wind turbine concept Presentation outline Extreme-scale Issues & Force alignment Morphing Pre-Alignment Tower Shadow Issues
- 3. 3 Extreme-Scale Issues & Force Alignment
- 4. 4 Integral blades (single piece) become more and more difficult to fabricate, transport, and install as extreme scales are approached (R = 120 m)
- 5. 5 Increasing sizes lead to increasing mass & increasing exponents (2.5+) once gravity loads start to dominate Can load alignment help reduce mass?
- 6. Bio-Inspiration 6 Palm trees have a light segmented trunk that bends downstream – load-alignment which reduce cantilever aerodynamic loads (vs. “stiff” strategy of an oak tree) 6
- 7. 7 Wind Turbine Forces Conventional vs. Load- Aligned Load combination of centrifugal (C), gravity (G), and thrust (T) aligned along the blade path via downwind coning
- 8. 8 Load Path Angle Conventional scales accommodate with pre-cone & shaft-tilt but angles are high at extreme scale, indicating potential benefits of downwind alignment (and perhaps of teetering)
- 9. 9 Morphing
- 11. 11 Load Path Angle as a function of Speed Small benefit for small turbines but significant load-path angles at larger scale, indicating potential benefits of alignment (and perhaps importance of teetering for downwind)
- 12. 12 First-Order Finite Element Analysis NREL 5 MW baseline upscaled to 10 MW with a radius of 82 m Used to compare to morphing & pre-aligned concepts Blade mass = 35,800 kg Material = based on E-LT-5500 fiberglass ( Modulus of elasticity = 41.8 GPa Poisson’s ratio = 0.28 Density = 1920 kg/m3
- 13. 13 Von-Mises Stresses Conventional (35.6 Mg) Fixed-Mass (35.6 Mg) Reduced-Mass (17.8 Mg) & Increased Length
- 14. 14 Increasing Length Benefits Morphing increases capture area below rated; makes up for losses due to coning; advantage will increase as size increases
- 15. 15 Conclusions for Steady-State Morphing Analysis But … Dynamics, Gusts and Fatigue tend to drive structural mass and so the above savings my be lost or only partially rHeianlgizinegd & Actuating Rotor Blades also introduces additional control complexity and hub design complexity
- 16. 16 Pre-Aligned
- 17. 1177 Pre-Aligned in Nature Fix load alignment to reduce cantilever moments (some aero-elastic flexing to adapt even further but no hinges)
- 18. 18 Fixed Mass Pre-Aligned Blade Zero moment nodes induced over 4 segments by setting proper alignment angles such that resultant force of each segment is tension aligned
- 19. 19 Tower Shadow Issues
- 20. Aerodynamically faired shroud around tower to substantially reduce wake effects and thus blade fatigue, and uses passive shroud alignment for yaw 20
- 21. Previous Studies Cylinder drag reduction w/ flow control: Lee et al. (2004) Hwang and Yang (2007) Sosa et al. (2009) Triyogi et al. (2009) Mashud et al. (2010) Blade active load control: Baker et al. (2007) Cooperman et al. (2013) Faired wind turbine tower: Hand et al. (2001) Janajreh et al. (2010) 21
- 22. Drag Reduction for an Inscribed Diameter 1 0.8 0.6 0.4 0.2 0 0 0.2 0.4 0.6 0.8 1 Cd,D D/c (ReD=1x105) Ellipse 1e5) NACA Airfoil (ReD=1x105) 1e5) NACA Airfoil (ReD=8.3e6) Cylinder with flow control 8.3x106) Cylinder with no flow control Airfoils have much lower drag than ellipses or cylinder 22 Cd,D º Fd ' 1 2rV2D Minimum drag for ~ 3:1 chord-to-thickness ratio
- 23. Select Pressure Distributions α = 0°, 3% Fixed Transition -1.5 -1 -0.5 Cp x/c 0 0.5 1 0 0.2 0.4 0.6 0.8 1 NACA0033 E862 E863 C30u C31u 23
- 24. PIV Setup 24 Flow Direction Y X Interrogation Window Laser Sheet Spherical and Cylindrical Lenses Mirror Model Laser Source
- 25. u Velocity Profile (X = 2D) 25 E863 C30u C30u but at 10° Cylinder
- 26. 26 or Self-yawing tripod for off-shore Downwind rotor on a floating tripod with cabling for yaw so downwind force aligns turbine to the wind and truss structure reduces net tower wake Cabled Pad
- 27. 27 CONCLUSIONS Steady-state analysis for morphing concept may allow substantial reductions in structural blade and tower mass at extreme-scales; but, hinge system may be heavy & complex Pre-alignment reduces complexity while retaining most of load savings; however, still have shadow effects Aerodynamic shrouds can dramatically reduces wake effects; however, wind angle changes effects and downwind tower loads may be problematic Much more work needed to determine relative feasibility for force-aligned downwind systems
Editor's Notes
- #2: OLD ACRONYM OF SUFAR
- #9: wind gradient - avoiding cyclic appearance of cantilever loads while maintaining a fixed rotor geometry with respect to the hub, e.g. individual pitch control, blade flapping, hub teetering with 2 blade
- #11: compare this to a stiffer oak tree that is uprooted in a hurricane
- #12: wind gradient - avoiding cyclic appearance of cantilever loads while maintaining a fixed rotor geometry with respect to the hub, e.g. individual pitch control, blade flapping, hub teetering with 2 blade
- #15: wind gradient - avoiding cyclic appearance of cantilever loads while maintaining a fixed rotor geometry with respect to the hub, e.g. individual pitch control, blade flapping, hub teetering with 2 blade
- #16: wind gradient - avoiding cyclic appearance of cantilever loads while maintaining a fixed rotor geometry with respect to the hub, e.g. individual pitch control, blade flapping, hub teetering with 2 blade
- #18: compare this to a stiffer oak tree that is uprooted in a hurricane
- #19: allows for simpler joint design In order to determine the alignment angles, the blade was segmented into four sections. For each segment, the total aerodynamic, centrifugal, and gravitational forces were calculated and assumed to act at the center of each section. Using the force values, the angle at each joint was set so that the net downstream moment at the node points was zero,
- #21: The geometric downwind curvature also helps alleviate the tower shadow wake effects since the blade tips (where the effect can be most problematic) are shifted far downstream of the tower from pre-alignment
- #27: may also help reduce wake effects since the increased stiffness associated with a broader platform allows smaller elements