Development of a Three-Dimensional Model for the Darrieus Rotor and Its Wake

A computational procedure suitable for simulating the flowfield, performance, and interference of a curvedbladed, three-dimensional Darrieus wind turbine is presented. The rotor blades are modeled as time-averaged sources in the steady, laminar momentum equations solved on a Cartesian grid. As an illustration of the potential of the method, terrain and generator box influence on the behavior of the turbine are simulated in a uniform freestream wind. The generator box of the turbine is modeled as a solid cube and viscous no-slip boundary conditions are prescribed on the generator box and the ground plane. The influence of the terrain on the flowfield of the turbine is considered for two hypothetical, two-dimensional ridge-lines. Computed turbine performance, such as the power coefficient and the normal force coefficient, are compared with results from Sandia field tests and a theoretical method based on stream-tube momentum balance for a stand-alone turbine. Quantitative differences in the performance of the Sandia 17-m turbine with and without the hypothetical terrains are discussed. Qualitative behavior of the flowfield under the influence of the ground plane is also presented with the help of velocity vector plots and path lines.