Wind field analysis over the complex terrain

Abstract

The topography effect on the wind characteristic of the atmospheric boundary layer (ABL) above the ground has attracted great attention in recent years become of the complex nonlinear interaction mechanisms between the topography and the wind field. In the wind turbine layout optimization analysis, the wind acceleration effect at the windward side of the hill could improve the wind turbine performance, while the flow separation region behind the hilltop is not a good choice for wind turbine installation. As to the slender building wind-resistance research, too many high-rise skyscrapers in the downtown area make the fluctuating velocity and wind load in the urban area hard to calculate. Therefore, it is essential to conduct the wind-terrain interaction analysis to explore the mechanism of it. The primary research goal of this task is to build a high-fidelity computational domain dynamics (CFD) simulation model to precisely describe the nonlinear wind-topography interaction characteristic. To efficiently solve the wind field in an acceptable time while maintaining a high prediction accuracy, the standard RANS k- epsilon model and the transient Re-Normalization Group (RNG) k-epsilon model is selected to resolve the turbulence flow in the mountainous and urban areas. The urban mesh is generated and refined at the surface of the geometry through the SnappyHexMesh module. As to the wind turbine wake pattern analysis above the hilly region part, an innovative wake modification method applied for the single wind turbine condition over a series of shape terrain has been proposed and validated with the CFD benchmark. For the multi-turbine complex terrain condition, the linear wake superposition model coupled with the proposed wake modification method is used to predict the performance of four turbines over a gaussian shape terrain under two inflow conditions. The urban wind environment and the pressure distribution on the surface of the highly sheltered bridge in the downtown area are also studied through the numerical simulation method. The 120-year return-period inflow speed and TI are derived based on the Gumbel distribution method and the HKO wind station data. Two wind stations' wind record data are introduced to validate the simulation model in this thesis. The mean pressure and gust pressure differences in the vertical and horizontal direction on the cross-section of the flyover are calculated. In terms of academic outcomes, the wind turbine test proposes a novel wake model that can accurately predict the wake speed and the added TI pattern above the hilly region in an acceptable time. The multi-turbine test exhibits considerable potential to extend the proposed model to the 3-D terrain condition and the wind farm layout optimization work. While for the urban environment study, research shows that the old extreme pressure principles in the highway design manual are too conservative. A new extreme pressure result under various exposure levels is proposed and acted as the suggestion for the highway department to update a new version structure design manual.