Numerical Studies Of The Wind Resource Characteristic Of Wind Farm On Complex Terrain

In wind farm micro-siting, wind resource is first to computed, and then the configuration of wind turbines is decided based on wind resource distribution result. The more wind resource distribution result is close to the actual distribution, the better the wind turbine arrangement will be. The right wind resource distribution can maximize the usage of wind energy, and avoid bad flow area to ensure wind turbine running life. Nowadays, more and more wind farms are built in complex terrain in which the flow is very complicated. This poses a challenge for wind farm wind resources calculation, because the traditional linear model calculation method is not applicable to complex terrain. Compared with the linear method, the CFD method which is based on nonlinear model can well reproduce the flow over complex terrain. And wind resource calculation based on CFD method can better capture the actual wind distribution. Therefore, it is significant to carry out the CFD simulation study for wind farms on complex terrain.In order to apply the CFD method in wind farm wind calculation and wind resources analysis, paper work first simulated the flat terrain and Askervein hill as research objects, to validate a RANS simulation method which is suitable for complex terrains. Based on the method, a wind resource calculation method was proposed, which included wind farm terrain processing, computational domain generation, wind CFD simulation results processing for multiple wind directions, analysis of flow field, and many other problems. After that, for unsteady flow characteristics in complex terrain, DES simulation method was applied to complex terrain simulation. First the flow over a cubic was simulated as the method validation, and then Bolund island was simulated to explore the flow characteristics in the complex terrain and DES numerical properties.The flow over wind farms is always fully developed turbulent boundary layer flow, comparing with the normal industrial flow. Firstly, in order to use standard k-e turbulence model with wall function, which is widely used in industry, in the simulation of wind farm with the complex terrain, wind flow over a flat terrain is simulated, to investigate the influence of some parameters in the standard k-e turbulence model with standard wall functions on the simulation of homogenous atmosphere. Then, Askervein hill is numerically simulated with the modified parameters in turbulence model and the results are compared with experiment.In order to use this method above in the wind resources assessment and micro-siting of wind farm in the complex terrain, in this paper, Island Nanao was simulated in wind directions at intervals of 30 degrees, under the assumption of neutral condition, to investigate the influence of inlet condition on the results. The simulation results show that the wind speed-up and intensity doesn’t change essentially under different inlet condition. Based on this law, with whole year wind data, a wind resource calculation method has been built, providing a strong reference for engineering practice.The flow structure is complicated in complex terrain, sometimes with distinctive unsteady flow characteristics. In order to use DES with wall function in the numerical simulation of wind farms with the complex terrain, first, the flow over a cube within full developed boundary layer was simulated using DES as the validation of the method. The quantities and flow fields on the symmetry streamwise plane were analyzed, and complex horseshoe vortex system was also observed at Reynolds number of 40000. The system consists of developing vortex, primary vortex, and corner vortex which are clockwise-rotating, and other induced counter-rotating vortices. For the first time put forward that, in a breaking away cycle, a new developing vortex does not develop upstream of the old developing vortex itself. Instead, it is the rest part of the old developing vortex after primary vortex breaking away, with breaking process developing from two sides to the center. Then, Bolund Island with an almost vertical upstream escarpment was simulated using DES with wall function. Computational domains with different density were utilized. Flow structure details and good results can be obtained when the grid size is a twentieth or smaller than the height of the island in large separation region, when using central scheme. DES has better performance than RANS in large separation region.