Title: HELICOIDAL%20VORTEX%20MODEL%20FOR%20WIND%20TURBINE%20AEROELASTIC%20SIMULATION%20Jean-Jacques%20Chattot%20University%20of%20California%20Davis%20OUTLINE
1HELICOIDAL VORTEX MODEL FOR WIND TURBINE
AEROELASTIC SIMULATIONJean-Jacques
ChattotUniversity of California DavisOUTLINE
- Challenges in Wind Turbine Flows
- The Analysis Problem and Simulation Tools
- The Vortex Model
- The Structural Model
- Some Results
- Conclusions
Fourth M.I.T. Conference June 13-15, 2007
2CHALLENGES IN WIND TURBINE FLOW ANALYSIS
- Vortex Structure
- - importance of maintaining vortex structure
10-20 D - - free wake vs. prescribed wake models
- High Incidence on Blades
- - separated flows and 3-D viscous effects
- Unsteady Effects
- - yaw, tower interaction, earth boundary layer
- Blade Flexibility
3THE ANALYSIS PROBLEM AND SIMULATION TOOLS
- Actuator Disk Theory (1-D Flow)
- Empirical Dynamic Models (Aeroelasticity)
- Vortex Models
- - prescribed wake equilibrium condition
- - free wake
- Euler/Navier-Stokes Codes
- - 10 M grid points, still dissipates wake
- - not practical for design
- - expensive to couple with structural model
- Hybrid Models
4REVIEW OF VORTEX MODEL
- 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
5GOLDSTEIN MODEL
Vortex sheet constructed as perfect helix with
variable pitch
6SIMPLIFIED 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
7ULTIMATE WAKE EQUILIBRIUM CONDITION
Induced axial velocity from average power
8BASE HELIX GEOMETRY USED FOR STEADY AND UNSTEADY
FLOWS
Vorticity is convected along the base helix, not
the displaced helix, a first-order approximation
9APPLICATION OF BIOT-SAVART LAW
10BLADE ELEMENT FLOW CONDITIONS
112-D VISCOUS POLAR
S809 profile at Re500,000 using XFOIL linear
extrapolation to
12CONVECTION IN THE WAKE
- Mesh system stretched mesh from blade
- To x1 where
- Then constant steps to
- Convection equation along vortex filament j
- Boundary condition
13CONVECTION IN THE WAKE
14ATTACHED/STALLED FLOWS
Blade working conditions attached/stalled
15RESULTS STEADY FLOW
Power output comparison
16RESULTS YAWED FLOW
Time-averaged power versus velocity at different
yaw angles
10 deg
5 deg
20 deg
30 deg
17STRUCTURAL MODEL
- Blade Treated as a Nonhomogeneous Beam
- Modal Decomposition (Bending and Torsion)
- NREL Blades Structural Properties
- Damping Estimated
18NREL BLADES
- Structural Coefficients
- - M5 kg/m
- - EIx800,000 Nm2
- - cfb4
- First Mode Frequency
- - f17.28 Hz (vs. 7.25 Hz for NREL blade)
19TIME AND SPACE APPROACHES
- Typical Time Steps
- - Taero0.0023 s (1 deg azimuthal angle)
- - Tstruc0.00004 s (with 21 points on blade)
- Explicit Scheme
- Large integration errors due to drifting
- Implicit Scheme
- Second-Order in time unstable
- First-order not accurate enough
- Modal Decomposition
- Very accurate. Integration error only in source
term
20NREL ROOT FLAP BENDING MOMENT COMPARISONV5 m/s,
yaw10 deg
21TOWER SHADOW MODELDOWNWIND CONFIGURATION
22TOWER SHADOW MODEL
- Model includes Wake Width and Velocity Deficit
Profile, Ref Coton et Al. 2002 - Model Based on Wind Tunnel Measurements
Ref Snyder and Wentz
81 - Parameters selected
- Wake Width 2.5 Tower Radius, Velocity Deficit 30
23SOME RESULTS
- V5 m/s, Yaw0, 5, 10, 20 and 30 deg
- V10 m/s, Yaw0 and 20 deg
- V12 m/s, Yaw0, 10 and 30 deg
- Comparison With NREL Sequence B Data
24RESULTS FOR ROOT FLAP BENDING MOMENTV5 m/s,
yaw0 deg
25RESULTS FOR ROOT FLAP BENDING MOMENTV5 m/s,
yaw5 deg
26RESULTS FOR ROOT FLAP BENDING MOMENTV5 m/s,
yaw10 deg
27RESULTS FOR ROOT FLAP BENDING MOMENTV5 m/s,
yaw20 deg
28RESULTS FOR ROOT FLAP BENDING MOMENTV5 m/s,
yaw30 deg
29NREL ROOT FLAP BENDING MOMENT COMPARISONV10
m/s, yaw0 deg
30NREL ROOT FLAP BENDING MOMENT COMPARISONV10
m/s, yaw20 deg
31NREL ROOT FLAP BENDING MOMENT COMPARISONV12
m/s, yaw0 deg
32NREL ROOT FLAP BENDING MOMENT COMPARISONV12
m/s, yaw10 deg
33NREL ROOT FLAP BENDING MOMENT COMPARISONV12
m/s, yaw30 deg
34CONCLUSIONS
- Stand-alone Navier-Stokes too expensive,
dissipates wake, cannot be used for design or
aeroelasticity - Vortex Model simple, efficient, can be used for
design and aeroelasticity - Remaining discrepancies possibly due to tower
motion
35HYBRID 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
36HYBRID METHODOLOGY
37RECENT PUBLICATIONS
- J.-J. Chattot, Helicoidal vortex model for
steady and unsteady flows, Computers and Fluids,
Special Issue, 35, 742-745 (2006). - 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). - J. M. Hallissy, J.J. Chattot, Validation of a
helicoidal vortex model with the NREL unsteady
aerodynamic experiment, CFD Journal, Special
Issue, 14236-245 (2005). - S. H. Schmitz, J.-J. Chattot, A parallelized
coupled Navier-Stokes/Vortex-Panel solver,
Journal of Solar Energy Engineering, 127475-487
(2005). - J.-J. Chattot, Extension of a helicoidal vortex
model to account for blade flexibility and tower
interference, Journal of Solar Energy
Engineering, 128455-460 (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, 128445-454 (2006). - J.-J. Chattot, Helicoidal vortex model for wind
turbine aeroelastic simulation, Computers and
Structures, to appear, 2007.
38APPENDIX AUAE Sequence QV8 m/s Dpitch18 deg
CN at 80
39APPENDIX AUAE Sequence QV8 m/s Dpitch18 deg
CT at 80
40APPENDIX AUAE Sequence QV8 m/s Dpitch18 deg
41APPENDIX AUAE Sequence QV8 m/s Dpitch18 deg
42APPENDIX BOptimum Rotor R63 m P2 MW
43APPENDIX BOptimum Rotor R63 m P2 MW
44APPENDIX BOptimum Rotor R63 m P2 MW
45APPENDIX BOptimum Rotor R63 m P2 MW
46APPENDIX BOptimum Rotor R63 m P2 MW
47APPENDIX BOptimum Rotor R63 m P2 MW
48APPENDIX BOptimum Rotor R63 m P2 MW
49APPENDIX CHomogeneous blade First mode
50APPENDIX CHomogeneous blade Second mode
51APPENDIX CHomogeneous blade Third mode
52APPENDIX CNonhomogeneous blade M distribution
53APPENDIX CNonhomog. blade EIx distribution
54APPENDIX CNonhomogeneous blade First mode
55APPENDIX CNonhomogeneous blade Second mode
56APPENDIX CNonhomogeneous blade Third mode
57APPENDIX D NONLINEAR TREATMENT
- Discrete equations
- If
- Where
58APPENDIX D NONLINEAR TREATMENT
- If
- is the coefficient of artificial
viscosity - Solved using Newtons method