Wind Turbine Micro-Siting Analysis at Vestas Wind Systems
Gregory S. Oxley, Ph.D
As a leader in wind energy, Vestas Wind Systems A/S, has installed over 41,000 turbines in 65 countries across five continents, and they continue to install wind turbines worldwide at the rate of one every four hours. Their goal is to help wind meet more than 10 percent of the world's energy needs by the year 2020.
The plant siting and forecasting group within Vestas employs meteorologists, applied mathematicians, computational fluid dynamics (CFD) specialists, engineers, and technicians to optimize wind power production while minimizing unfavorable loads on wind turbines. Using wind and local terrain data and turbulence and shear inflow characteristics, they check geographic site influence on local wind turbine loads and try to minimize bad wind risks using an automated CFD analysis system that incorporates Pointwise for grid generation and STAR-CCM+ for flow solution.
The process starts with an industry standard elevation contour map, which is converted to PLOT3D format for import into Pointwise as a database geometry as shown in Figure 1.
Figure 1: Terrain contour data is converted to PLOT3D for import to Pointwise. (large image)
After import to Pointwise, an automated Glyph script creates connectors on database surfaces, constructs terrain smoothing extensions at the boundaries of the domain, determines the number of grid points to use based on desired spatial resolution, creates a 3D structured grid block using hyperbolic extrusion, and exports the resulting mesh as a PLOT3D file.
Then another script is run to convert the structured volume mesh to a hanging node configuration and convert to STAR-CCM+ format as shown in Figure 2.
Figure 2: Hyperbolic extruded grid is converted to hanging node configuration. (large image)
Next, the grid is imported into STAR-CCM+ and flow solutions are computed for a matrix of wind directions and velocities. The results are postprocessed and compiled into PowerPoint and Excel reports to provide a variety of data that are then automatically emailed to engineers. An example of this type of data, contours of turbulence intensity at the height of the wind turbine hub for two wind directions, is shown in Figure 3.
Figure 3: Turbulence intensity plots are used to assess loads on wind turbines. (large image)
This highly-automated process has allowed CFD to become a crucial step in the wind turbine siting process at Vestas. This steady analysis provides engineers with good insight into turbulence and wind shear and veer properties of a wind park, which leads to decisions on where to place wind turbines. It can also lead to more advanced unsteady simulations to perform wind park forensics for more problematic sites. Pointwise has helped to enable this process by quickly producing high quality grids as part of an automated process.