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Challenges in Wind Turbine Flows The Analysis Problem and Simulation Tools

Explore the challenges and methods in wind turbine aerodynamics through vortex models, hybrid approaches, and simulation tools. Learn about vortex structuring, blade flexibility, wake effects, and more.

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Challenges in Wind Turbine Flows The Analysis Problem and Simulation Tools

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  1. NUMERICAL SIMULATION OF WIND TURBINE AERODYNAMICSJean-Jacques ChattotUniversity of California DavisOUTLINE • Challenges in Wind Turbine Flows • The Analysis Problem and Simulation Tools • The Vortex Model for Analysis and Design • The Hybrid Approach • Conclusion Stanford Tuesday, May 6, 2008

  2. CHALLENGES IN WIND TURBINE FLOW ANALYSIS AND DESIGN • Vortex Structure - importance of maintaining vortex structure 10-20 R - free wake vs. prescribed wake models - nonlinear effects on swept tips and winglets • High Incidence on Blades - separated flows and 3-D viscous effects • Unsteady Effects - yaw, tower interaction, earth boundary layer • Blade Flexibility

  3. CHALLENGES IN WIND TURBINE FLOW ANALYSIS

  4. CHALLENGES IN WIND TURBINE FLOW ANALYSIS

  5. THE ANALYSIS PROBLEM AND SIMULATION TOOLS • Actuator Disk Theory (1-D Flow) • Empirical Dynamic Models (Aeroelasticity) • Vortex Models - prescribed wake + equilibrium condition - free wake - applied to design of blades for maximum power at given thrust on tower (including sweep and winglets) • Euler/Navier-Stokes Codes - 10 M grid points, still dissipates wake - not practical for design

  6. THE VORTEX MODEL FOR ANALYSIS AND DESIGN • Goldstein Model • Simplified Treatment of Wake • Rigid Wake Model • “Ultimate Wake” Equilibrium Condition • Base Helix Geometry Used for Steady and Unsteady Flows • Application of Biot-Savart Law • Blade Element Flow Conditions • 2-D Viscous Polar

  7. GOLDSTEIN MODEL Vortex sheet constructed as perfect helix with variable pitch

  8. SIMPLIFIED TREATMENT OF WAKE • No stream tube expansion, no sheet edge roll-up (second-order effects) • Vortex sheet constructed as perfect helix called the “base helix” corresponding to zero yaw

  9. “ULTIMATE WAKE” EQUILIBRIUM CONDITION Induced axial velocity from average power (iterations):

  10. VWind = 7m/s INFLUENCE OF WAKE ON RESULTS

  11. BASE HELIX GEOMETRY USED FOR STEADY AND UNSTEADY FLOWS Vorticity is convected along the base helix, not the displaced helix, a first-order approximation

  12. 2-D VISCOUS POLAR

  13. ANALYSIS RESULTS: STEADY FLOW Power output comparison

  14. YAWED FLOW Time-averaged power versus velocity at different yaw angles =10 deg =5 deg =20 deg =30 deg

  15. TOWER INTERFERENCE MODEL • Simplified Model • NREL Root Flap Bending Moment Comparison • - Effect of Incoming Velocity V=5, 8 and 10 m/s • - Effect of Yaw yaw=5, 10 and 20 deg

  16. “UPWIND” CONFIGURATION

  17. NREL ROOT FLAP BENDING MOMENT COMPARISONV=5 m/s, yaw=20 deg

  18. DESIGN METHODOLOGY • Minimize Torque Coefficient Thrust Coefficient is Lagrange multiplier

  19. DESIGN METHODOLOGY • Given “adv” – Given profile (2-D viscous polar) or corresponding to • Optimum circulation • Design:

  20. Vortex Line Method (VLM) – Operating Points DESIGN AND ANALYSIS OF A ROTOR BLADE DESIGN TEST CASE

  21. HYBRID APPROACH • Use Best Capabilities of Physical Models • - Navier-Stokes for near-field viscous flow • - Vortex model for far-field inviscid wake • Couple Navier-Stokes with Vortex Model • - improved efficiency • - improved accuracy

  22. HYBRID METHODOLOGY Navier-Stokes Biot-Savart Law (discrete) Boundary of Navier-Stokes Zone Vortex Method Bound Vortex Converged for … Vortex Filament Coupling Methodology

  23. PCS/VLM COMPARISON Optimum Blade designed with VLM VLM PCS Thrust [N] 509.62 508.31 Tangential Force [N] -183.63 -179.89 Bending Moment [Nm] 1803.1 1814.8 Torque [Nm] -588.82 -583.80 Power [kW] 8.879 8.804 Difference in Power : 0.84 %

  24. RESULTS: STEADY FLOWNREL ROTOR Power output comparison

  25. PCS k-ω : Γj PCS k-ω : cl VLM : Γj VLM : cl PCS/VLM COMPARISON

  26. Trailing Vorticity is traceable with the spanwise velocity component at 5%-10% chord length downstream of the blade’s trailing edge. These complex 3D effects are very difficult to detect with ‘strip theory’. The PCS solver on the other hand is capable of disclosing such phenomena close to Peak Power. VWind = 7m/s VWind = 9m/s VWind = 10m/s VWind = 11m/s TRAILING VORTICITY NEAR PEAK POWER

  27. CONCLUSIONS • Vortex Model: simple, efficient, can be used for design • Stand-alone Navier-Stokes: too expensive, dissipates wake, cannot be used for design • Hybrid Model: takes best of both models to create most efficient and reliable simulation tool • Next Frontier: aeroelasticity and multidisciplinary design

  28. RECENT PUBLICATIONS • S. H. Schmitz, J.-J. Chattot, “A coupled Navier-Stokes/Vortex-Panel solver for the numerical analysis of wind turbines”, Computers and Fluids, Special Issue, 35: 742-745 (2006). • S. H. Schmitz, J.-J. Chattot, “A parallelized coupled Navier-Stokes/Vortex-Panel solver”, Journal of Solar Energy Engineering, 127:475-487 (2005). • J.-J. Chattot, “Extension of a helicoidal vortex model to account for blade flexibility and tower interference”, Journal of Solar Energy Engineering, 128:455-460 (2006). • S. H. Schmitz, J.-J. Chattot, “Characterization of three-dimensional effects for the rotating and parked NREL phase VI wind turbine”, Journal of Solar Energy Engineering, 128:445-454 (2006). • J.-J. Chattot, “Helicoidal vortex model for wind turbine aeroelastic simulation”, Computers and Structures, 85:1072-1079 (2007). • S. H. Schmitz, J.-J. Chattot, “A method for aerodynamic analysis of wind turbines at peak power”, Journal of Propulsion and Power, 23(1):243-246 (2007). • J.-J. Chattot, “Effects of blade tip modifications on wind turbine performance using vortex model”, AIAA 2008-1315 (2008).

  29. APPENDIX AUAE Sequence QV=8 m/s Dpitch=18 deg CN at 80%

  30. APPENDIX AUAE Sequence QV=8 m/s Dpitch=18 deg CT at 80%

  31. APPENDIX AUAE Sequence QV=8 m/s Dpitch=18 deg

  32. APPENDIX AUAE Sequence QV=8 m/s Dpitch=18 deg

  33. APPENDIX BOptimum Rotor R=63 m P=2 MW

  34. APPENDIX BOptimum Rotor R=63 m P=2 MW

  35. APPENDIX BOptimum Rotor R=63 m P=2 MW

  36. APPENDIX BOptimum Rotor R=63 m P=2 MW

  37. APPENDIX BOptimum Rotor R=63 m P=2 MW

  38. APPENDIX BOptimum Rotor R=63 m P=2 MW

  39. APPENDIX BOptimum Rotor R=63 m P=2 MW

  40. APPENDIX CHomogeneous blade; First mode

  41. APPENDIX CHomogeneous blade; Second mode

  42. APPENDIX CHomogeneous blade; Third mode

  43. APPENDIX CNonhomogeneous blade; M’ distribution

  44. APPENDIX CNonhomog. blade; EIx distribution

  45. APPENDIX CNonhomogeneous blade; First mode

  46. APPENDIX CNonhomogeneous blade; Second mode

  47. APPENDIX CNonhomogeneous blade; Third mode

  48. TOWER SHADOW MODELDOWNWIND CONFIGURATION

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