Effects Of Upstream Atmospheric Boundary Layer Flow On The Wind Fields Over The Idealized Hill Using Large-eddy Simulation

The development of onshore wind farms in China is beneficial to the transformation and upgrading of energy consumption patterns and the improvement of environmental protection.In addition,it is also conducive to the reasonable utilization of land surface and the comprehensive implementation of sustainable development strategy.However,due to effects of surface roughness,hill slope and hill shape,the atmospheric boundary layer(ABL)turbulent flow over hilly terrain involves many complicated flow phenomena,i.e.,turbulence intermittency,flow separation and reattachment,and vortex shedding.The aforementioned flow regimes result in the inhomogeneity and non-Gaussianity of the wind speed distribution,which further leads to the large errors between the evaluation results of wind energy resources and the actual power generation of wind farms.Therefore,the accurate prediction of the turbulent flow fields over mountainous areas is of great importance for the efficient use of wind resource and the high-quality development of wind farm.Based on the large-eddy simulation(LES)turbulence model,the turbulent flow fields over hilly terrain are systematically investigated in this thesis.The inflow turbulence generation(ITG)methods and sub-grid scale(SGS)models are crucial to the prediction accuracy of LES.Hence,based on the comparative study of different ITG approaches and SGS models,the refined numerical modeling framework is proposed in the context of flow fields over idealized hills.Additionally,wind shear coefficient(WSC)and turbulence intensity(TI)are key parameters of atmospheric boundary layer flow.Therefore,grounded on the proposed framework,the effects of upstream atmospheric boundary layer flow on the wind fields over idealized hilly terrain ae clarified.The main research contents are summarized as follows:(1)The fundamental theories and key techniques of LES turbulence model are elaborated.Besides,the rationale and evolution of different ITG methods are introduced.Moreover,the advantages and limitations of these approaches are comparatively analyzed.Furthermore,several prospects for future research regarding to the ITG approaches are proposed.(2)The wind tunnel replication method and the consistent discretizing random flow generation(CDRFG)method are employed to simulate the ABL flows over standard terrains specified in Chinese building code,respectively.To validate and discuss the rationality and feasibility of different ITG methods,the comparative analysis is carried out from the aspects of statistical characteristics,flow field structures and computational efficiency.Moreover,the mesh scheme of LES for the generation of ABL flow fields is proposed.(3)To establish the refined numerical simulation framework of turbulent flow fields over idealized hills,the performance of ITG approaches and SGS models on the LES prediction are examined and compared in the context of a smooth 2-D ridge and a smooth3-D hill.Additionally,for the purpose of developing the evaluation system,the characteristics of turbulent flows over idealized hills are assessed and analyzed from the aspects of turbulent statistics and flow patterns.(4)The upstream ABL flows with different WSCs and TIs are simulated by CDRFG method.Based on the refined numerical modeling approach and evaluation criteria proposed in this thesis,the turbulent flow fields over 3-D hills with different slopes are investigated to clarify the coupling mechanism between the ABL approaching flows and the turbulent flow fields over hilly terrain.