基于WRF-LES模式的大气边界层近地风场精细化模拟研究

Refined Simulation of Near-Surface Wind Field of Atmospheric Boundary Layer Based on WRF-LES Model

台风等极端气象灾害对工程结构安全造成严重威胁,研究近地面大气边界层精细化模拟对于土木工程具有重要应用价值.数值天气预报系统(WRF)中的大涡模拟(LES)模块具有参数方案多、精度高等优点,适用于近地面风场精细化模拟,但数值天气预报-大涡模拟(WRF-LES)精细化模拟效果与参数设置密切相关.寻求适用于精细化模拟近地面风场的参数设置,选用WRF-LES模式中的几种次网格模型和空间差分格式,采用较细密的网格分辨率,进行理想大气边界层模拟.对比平均风速剖面、湍流强度剖面和功率谱等风场特性,讨论关键参数对近地面风场模拟精度的影响,确定合适的参数设置.研究表明:对次网格模型,非线性回波散射和各向异性(NBA1)模型可有效改善近地面风场模拟精度;对网格方案,在计算域底部不均匀加密垂直网格可更好地描述近地面风场空间分布特征,有效减小计算资源;对空间差分格式,偶数阶差分相较奇数阶差分格式可捕获更小尺度湍流结构.所提出的WRF-LES模式参数方案,可为精细化模拟近地面风场和台风边界层提供技术参考.

Extreme meteorological disasters such as typhoons pose a serious threat to the safety of engineering structures.Therefore,the refined simulation on the near-surface atmospheric boundary layer(ABL)is valuable for civil engineering.Large-eddy simulation(LES)implemented in the weather research and forecating(WRF)model has the advantages of multiple options of numerical schemes and high accuracy.It is generally suitable for the refined simulation of the near-surface wind field,although the performance of simulation results is closely related to the numerical methods.This paper assesses the impacts of vital parameters regarding subfilter-scale(SFS)stress models,mesh size,and spatial difference schemes within WRF-LES to simulate the ideal ABL in order to figure out appropriate numerical schemes for the refined simulation of the near-surface wind field.The wind field characteristics are addressed and analyzed such as mean wind speed profile,turbulence intensity profile,and power of spectrum.Comparisons of simulation results among different SFS stress models indicate that the nonlinear backscatter and anisotropy one(NBA1)SFS stress model can effectively improve the accuracy of simulation in the near-surface wind profiles.Investigations of mesh resolution effects indicate that the nonuniformly refined vertical grid near the surface agrees much better with the expected profiles and reduces the expenditure of computational resources.Furthermore,the results show that the even-order spatial difference schemes produce more small-scale turbulent structures than the odd-order difference schemes.The numerical methods of WRF-LES proposed can provide a technical reference for refined simulation of the near-surface wind field and typhoon boundary layer.