Global Flow Solutions Mark Zagar, Cheng Hu-Hu, Yavor Hristov, Søren Holm Mogensen, Line Gulstad Vestas Wind & Site Competence Centre, Technology R&D

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1 Global Flow Solutions Mark Zagar, Cheng Hu-Hu, Yavor Hristov, Søren Holm Mogensen, Line Gulstad Vestas Wind & Site Competence Centre, Technology R&D vestas.com

2 Outline The atmospheric modeling capabilities at Vestas Wind & Site Competence Centre CFD in the siting process Case studies Unsteady DES simulations Importance of atmospheric stability Merging of scales Concluding Remarks Brief look into the future 2 DANSIS Meeting, October 28,

3 Vestas Wind & Site Competence Centre Vestas Nacelles A/S Vestas Blades A/S Vestas Spare Parts A/S Vestas Towers A/S Vestas Control Systems A/S Vestas People & Culture Vestas Technology R&D Vestas Americas Vestas Northern Europe Vestas Mediterranean Vestas Central Europe Vestas Asia Pacific Vestas Offshore 3 DANSIS Meeting, October 28,

4 Vestas Wind & Site Competence Centre Vestas Wind & Site Competence Centre Siting & Load Applications Modelling, Statistics and Risk Analysis Global Flow Solutions 4 DANSIS Meeting, October 28,

5 Jetstream High performance blade clusters (1344 CPU cores) 2.7 TB ram 260 TB disk 8 meters long 9500 kg 250 kw power consumption 5 DANSIS Meeting, October 28,

6 Model-Portfolio Global scale NCAR CAM (Community Atmosphere Model) Global Ocean Wave Models Meso-Scale WRF (Weather Research and Forecasting Model) Research, special cases, LES and operational ETA model operational CFD STAR-CCM+ OpenFOAM 6 DANSIS Meeting, October 28,

7 Introduction Turbulence an important actor in the wind turbine business Wind turbine manufactures Product design Energy production estimate Service costs Customers Business case certainty? Lower cost of Energy Financing A growing market Best seats (sites) are taken Moving towards the edge of design limits fundamental understanding of atmospheric flow characteristics is crucial. 7 DANSIS Meeting, October 28,

8 CFD support: Mesh and boundary conditions WAsP Map Mesh Turbulence and wind rose Boundary conditions 8 DANSIS Meeting, October 28,

9 CFD support: VSC CFD functionality (RANS) Macro 2 Bash Script STAR-CCM+ Case i VSC STAR-CCM+ Import/Volume Meshing STAR-CCM+ Case i+1 Macro 2 CFD PDF & Excel Reports Macro 1 Macro 2 STAR-CCM+ Case N Queuing System 9 DANSIS Meeting, October 28,

10 CFD + VDC = Reducing Risk 10 DANSIS Meeting, October 28,

11 Validation with LIDAR Validation of the CFD is crucial. High frequency LIDAR (Light Detection and Ranging) measurements in controlled test case scenarios. Height (m) CFD MetMast Wind Speed (m/s) NNW (330) WNW (300) W (270) WSW (240) SSW (210) N (0) S (180) V_metmast V_CFD NNE (30) ENE (60) E (90) ESE (120) SSE (150) Velocity map TI map LIDAR Validation promotes confidence in the CFD tools and improved practice in their application. Improves specification of inlet conditions and turbulence modelling. 11 DANSIS Meeting, October 28,

12 Steady vs. Unsteady Simulations Steady state simulations provide time averaged data. Steady state assumes that the flow never changes at a point. Steady state simulations can underpredict zones of influence. Vortex Shedding Steady State Solution Unsteady Solution 12 DANSIS Meeting, October 28,

13 Turbulence Modelling Shift from RANS (Reynolds Averaged Navier Stokes) to methods such as LES (Large Eddy Simulation) or DES (Detached Eddy Simulation) DES= LES + RANS RANS model is used in near-wall region LES model is used in far field where large eddies are detached from the nearwall region Challenges Mesh is the foremost factor which determines the level of success Need enormous computing resources Typical Turbulence Spectrum Detached Eddy Simulation 13 DANSIS Meeting, October 28,

14 Why DES? Unsteady RANS (URANS) simulations are often failed to capture high-frequency fluctuating flows DES is sensitive to grid layout but it does not require very fine mesh near walls and usual RANS mesh work well to resolve the near wall region DES can resolve the flow phenomena of eddy breaks without losing significant details 14 DANSIS Meeting, October 28,

15 A Challenging Case 15 DANSIS Meeting, October 28,

16 Unsteady CFD 290 Wind direction 280 Wind direction (deg) Tim e (sec) 16 DANSIS Meeting, October 28,

17 The Importance of Atmospheric Stability An Initial Perturbation Stable Unstable Neutral Most CFD calculations assume neutral conditions. 17 DANSIS Meeting, October 28,

18 Downslope winds and extreme turbulence 3 factors determining the flow over a mountain barrier: Atmospheric stability Air flow, speed and direction Topographic characteristics of the barrier 18 DANSIS Meeting, October 28,

19 SE 500m A gap: channeling accelerating 500m Slope: accelerating! turbulence SE 19 DANSIS Meeting, October 28,

20 Example of an event Exactly the right combination of the three parameters. Stability wind speed and direction Mountain barrier Mast measurements: 20 DANSIS Meeting, October 28,

21 WRF-LES WRF V3.1.1 Real analyses (GFS) imposed at the outer boundary of the 27km nest subsequent nesting in ratio of 3 all the way to 37m simultaneous 111m and 37m LES enable easy comparison no information is lost as in a case of off-line LES 21 DANSIS Meeting, October 28,

22 Downslope acceleration & pulsations M 6 km 22 DANSIS Meeting, October 28,

23 Unique siting competence Mesoscale modelling Capture complex terrain Real weather conditions Long-term runs Extreme case studies Mesoscale Dimensions km Weather as we feel it Local wind systems Thunderstorms Down-scaling e.g. NCAR Low-frequency variability BUT seen as turbulence in the measurements CFD modelling Micro-scale terrain features Siting with precision Estimate and avoid extreme conditions 23 DANSIS Meeting, October 28,

24 Concluding Remarks CFD has become a standard tool for flow analysis in Vestas Wind & Site Competence Centre The DES method is able to capture transient flow phenomena like eddy breaks, flow separation, and unsteadiness of shear layer near walls. In addition to turbulence intensity, wind shear, wind veer and inflow angle unsteadiness also contribute to the determination of the wind turbine lifetime Unsteady CFD provides valuable input to load calculations and product development WRF-LES simulations proves the importance of including atmospheric stability in turbulence modelling. CFD Meso-Scale Models High Frequency Data Business case certainty! 24 DANSIS Meeting, October 28,

25 A brief look into the Future: Continously improve the automatic process Develop the link between CFD and Meso-Scale High focus on flow in forested areas! 25 DANSIS Meeting, October 28,

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