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Wind Modeling Studies by Dr. Xu at Tennessee State University

Wind Modeling Studies by Dr. Xu at Tennessee State University. Guanpeng Xu Tennessee State University Center of Excellence in Information System, Engineering & Management. Overview of Presentation. Wind Projects Methodologies Results and Conclusions. Wind Modeling Studies.

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Wind Modeling Studies by Dr. Xu at Tennessee State University

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  1. Wind Modeling Studies by Dr. Xu at Tennessee State University Guanpeng Xu Tennessee State University Center of Excellence in Information System, Engineering & Management

  2. Overview of Presentation • Wind Projects • Methodologies • Results and Conclusions

  3. Wind Modeling Studies • Computational Studies of Horizontal Axis Wind Turbines • Full NS • Hybrid Methodology • Overset Grid (CHIMERA) • 2D/3D Icing Simulation • 2D Icing • 3D Icing The first project is a part of my Ph.D. research. My advisor is Lakshmi Sankar at School of Aerospace Engineering, Georgia Institute of Technology Projects were supported by National Renewable Energy Laboratory (NREL), DOE

  4. Mathematical Formula Reynolds Averaged Navier-Stokes Equations in Finite Volume Representation: • Where q is the state vector. E, F, and G are the inviscid fluxes, and R, S, and T are the viscous fluxes • A finite volume formulation using Roe’s scheme is used. • The scheme is third order or fifth order accurate in space and second order accurate in time.

  5. N-S zone Potential Flow Zone Tip Vortex The Hybrid Methodology • The flow field is made of • a viscous region near the blade(s) • A potential flow region that propagates the blade circulation and thickness effects to the far field • A Lagrangean representation of the tip vortex, and concentrated vorticity shed from nearby bluff bodies such as the tower • This method is unsteady, compressible, and does not have singularities near separation lines

  6. The Overset Grid Methodology • Inclusion of tower effects requires modeling non-rotating and rotating components. • Georgia Tech CHIMERA methodology has been modified for tower shadow effects of HAWT : • Body-fitted grids are used for rotating blades and tower. • Each grid block is simulated using either a Navier-Stokes or hybrid method. • The flow fields among the grid sets are linked by 3-D interpolation.

  7. The Icing Simulation • Porous ice with liquid water content and air/vapor is assumed. • The flow field and icing/melting are calculated using a modular approach. • Grid is deformed with on-the-fly ice shape; NS solver is used for outer flow.

  8. Configuration Studied • NREL has collected extensive performance data for three rotor configurations: • A rotor with rectangular planform, untwisted blade and S-809 airfoil sections, called the Phase II Rotor • A twisted rotor, with rectangular platform and S-809 sections, called the Phase III Rotor • A two bladed, tapered and twisted rotor, called the Phase VI Rotor. Best quality measurements (wind tunnel) are available.

  9. Results and Discussion --Sample Grid • Size 11043402(380,000) • Viscous zone 6043202 (100,000) Body fitted grid on Phase II rotor

  10. OVERSET GRID A very coarse grid was used for Proof of Concept

  11. Results for the Phase II Rotor

  12. Results for the Phase III Rotor

  13. Results for the Phase VI Rotor Flap Bending Moment for One Blade

  14. Typical Natural 10m/s Inflow Wind

  15. Measured Power v.s. Time at 20 degree Yaw • Average values well predicted • Higher harmonics are not captured well, because we only model the first harmonic of the wind.

  16. Harmonic Analysis of the Calculated Power

  17. Flow Field May be Examined for Interesting Features The Upper Surface of the Phase II Rotor at 20 m/s

  18. Streamlines at a Typical Span Station of Phase II rotor at 20m/s

  19. Ice Shape after Half an Hour

  20. Tower Shadow Causes 15% Variation in Wind Speed 10m/s Portion of the Rotor Disk exposed to the tower wake ~8.5m/s • Code predicted this loss in dynamic pressure, but not the vortex shedding effects due to the sparse grid employed.

  21. Improvement to a Tip Loss Model and a Stall Delay Model Using CFD as a Guide Effects of Corrigan’s Model with Different values of n

  22. Conclusions • The Hybrid method, which solves the HAWT flow using a zonal approach, has been developed for efficiently simulating fully three-dimensional viscous fluid flow around an HAWT. Good results have been obtained. • A full Navier-Stokes methodology has also been developed. Two turbulence models and two transition prediction models have been integrated into above solvers. Consistent results have been obtained for above two solvers. An overset grid based version that can model rotor-tower interactions has been developed.

  23. Conclusions • The physics studied includes turbulence models, transition prediction models, yaw (unsteady) simulation, tower shadow, wind turbine flow states, stall delay, and tip losses. • The complete research activities have been documented in Guanpeng Xu’s doctoral thesis, Journal of Solar Energy Engineering, and in AIAA papers, 1999-0042, 2000-0048, 2001-0682, 2001-7796, and are omitted here.

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