1. CFD Simulation: MEXICO Rotor Wake
EWEC: 2009
Andreas Bechmann & Niels Sørensen
Risø DTU ∙ National Laboratory for Sustainable Energy

2. Outline: Background MEXICO Experiment CFD Simulations Conclusion
CFD Simulation of the MEXICO Rotor Wake
17 March 09

3. Background 1/3
“Today, siting of wind turbines in wind farms is based on power output considerations”
TOPFARM project: Optimization of wind farm topology based on power output and turbine loads.
WP1: Internal flow model
Model to describe the flow inside the wind farm
CFD Simulation of the MEXICO Rotor Wake
17 March 09

4. Background 2/3 Wind farm Wind tunnel Single wind turbine
How to validate the model?
Single wind turbine
Wind tunnel
CFD Simulation of the MEXICO Rotor Wake
17 March 09

5. Background 3/3 Wind tunnel The MEXICO Experiment Objectives:
Controlled conditions
PIV measure. 1.3D downstream
Open wind tunnel – tunnel effects?
Objectives:
To make a “clean” dataset for validating wake models
Method:
Extract wake data from the MEXICO experiment
Compare measurements with high resolution CFD
Combine measurements and CFD results in a dataset for validating wake models
Wind tunnel
CFD Simulation of the MEXICO Rotor Wake
17 March 09

6. Outline: Background MEXICO Experiment CFD Simulations Conclusion
Title of the presentation
17 March 09

7. MEXICO Exp. 1/4 MEXICO Info:
(pictures by ECN, NLR)
Model Experiments in Controlled Conditions
Purpose: ”measurements on wind turbine model including the near wake”
Large tunnel of DNW used
Many groups participated: ECN was coordinator
The Vindtunnel:
Open section 9.5×9.5m
Max. air speed 30 m/s
Balance (3 forces/moments)
CFD Simulation of the MEXICO Rotor Wake
17 March 09

8. MEXICO Exp. 2/4 The Rotor: 4.5m diameter 3 airfoils for each blade:
1. Root: DU 91-W2-250
2. Mid: RISØ A1-21
3. Tip: NACA
Zig-zag tape at 5% chord
Pitch angle -2.3 degrees
No signal from strain gages?
(global rotor forces are
estimated from the balance)
Pressure at 5 sections (25%,35%,60%,82%,95%)
CFD Simulation of the MEXICO Rotor Wake
17 March 09

9. MEXICO Exp. 3/4 Earlier CFD findings 1/10 scale of DNW wind tunnel
Niels N. Sørensen, Risø/DTU
MEXICO, 3. Progress Meeting,
Athens 28-29
Nov. 2001
Earlier CFD findings
1/10 scale of DNW wind tunnel
Clear tunnel effects in the far wake
Tunnel effects limited at the rotor
Doeke Rozendal
Flow field measurements on a small scale wind turbine model in the DNW PLST wind tunnel
NLR-CR
The PIV measurements:
PIV measuring sheet (34×40cm) placed horizontally at 270 deg azimuth
In phase with rotor (freq=3 rotor revolutions) for 40s (100 samples)
Axial traverse at r/R=0.82
Radial traverses from r/R=
-0.6D
-0.4D
0.3D
1.0D
1.3D
-1.0D
CFD Simulation of the MEXICO Rotor Wake
17 March 09

10. MEXICO Exp. 4/4 Selected data: 100 GB of data
Axi-symmetric cond. No yaw
Pitch angle -2.3 degree
425 rpm (tip speed 100m/s)
Wind speed: 10, 15, 24 m/s
(tip speed ratio 10, 6.7, 4.2)
CFD Simulation of the MEXICO Rotor Wake
17 March 09

11. Outline: Background MEXICO Experiment CFD Simulations Conclusion
CFD Simulation of the MEXICO Rotor Wake
17 March 09

12. The Simulations 1/5 CFD solver: EllipSys3D RANS: SST k-ω model
Fully turbulent
Steady-state simulations
Surface mesh:
All 3 blades meshed
256×64 cells on each
Volume mesh:
256 cells in normal direction
(~7 rotor diameters)
Wake resolved approx 3D
Wind tunnel is not included
CFD Simulation of the MEXICO Rotor Wake
17 March 09

13. The Simulations 2/5 Rotor forces:
Thrust. Estimated tower drag subtracted from balance force
Pressure distributions.
CFD Simulation of the MEXICO Rotor Wake
17 March 09

14. The Simulations 3/5 CFD Simulation of the MEXICO Rotor Wake
17 March 09

15. The Simulations 4/5 Wake results: -0.6D -0.4D 0.3D 1.0D 1.3D -1.0D
CFD Simulation of the MEXICO Rotor Wake
17 March 09

16. The Simulations 5/5 Validation dataset : Tunnel effects removed
Expands further downstream
Airfoil characteristics has been extracted which includes 3D effects
CFD Simulation of the MEXICO Rotor Wake
17 March 09

17. Outline: Background MEXICO Experiment CFD Simulations Conclusions
CFD Simulation of the MEXICO Rotor Wake
17 March 09

18. Thank you for listening!
Conclusions
Wake data extracted from MEXICO database
CFD simulations of MEXICO wake were performed
Measurements and simulations compare well
Only the near-wake was simulated (~3D) (due to mesh topology)
Simulations with laminar–turbulent transition could be interesting
A new validation dataset for wake models without tunnel effects
Thank you for listening!
CFD Simulation of the MEXICO Rotor Wake
17 March 09