CFD Simulation: MEXICO Rotor Wake EWEC: 2009 Andreas Bechmann & Niels Sørensen Risø DTU ∙ National Laboratory for Sustainable Energy andh@risoe.dtu.dk

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

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

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

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

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

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

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 63-418 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

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-2003-485 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=0.5-0.9 -0.6D -0.4D 0.3D 1.0D 1.3D -1.0D CFD Simulation of the MEXICO Rotor Wake 17 March 09

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

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

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

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

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

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

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

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

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