基于NSRFG方法的标准地貌风场大涡模拟研究

RESEARCH ON NSRFG-BASED LES SIMULATION FOR STANDARD WIND TERRAINS

大涡模拟中入流湍流的准确模拟,是计算风工程领域当前研究的热点;准确定义与各类地貌大气边界层湍流特征相符的入流边界条件,是进行建筑结构风效应研究的前提(也是当前研究的难题)。该文在新提出的以湍流合成法为基础的LES入流湍流生成技术——NSRFG方法上,研究了数学模型中若干参数的适当取值问题。通过数值分析对采样频率间距Δƒ、引入的时间尺度因子τ0和空间尺度因子θ、衰减系数cj及调谐因子γj等重要参数进行敏感性研究,分析了上述参数的取值对所生成湍流脉动风速功率谱、均方值和空间相关性等模拟结果的影响;在此基础上建议了一套与中国规范四类标准地貌风场相对应的参数表,从而建立基于该方法的"标准数值风场模型";通过实例对四类标准地貌边界层湍流风场进行数值模拟和平衡态检验。研究表明:上述关键参数的赋值对采用NSRFG方法进行大气边界层湍流风场的重构影响显著,该文基于NSRFG方法所建议的标准地貌数值风场模型,对研究者采用LES进行结构风工程的数值模拟研究具有一定的参考价值。

Accurately simulating inflow turbulence for large eddy simulation(LES) is a hot topic in the field of computational wind engineering. Defining appropriate inflow boundary conditions in accordance with the turbulence characteristics of various atmospheric boundary layers(ABLs) is a prerequisite and indeed a great challenge in numerical research of wind effects on building structures at current stage. Based on the newly proposed LES inflow turbulence generation technology-NSRFG method, which belongs to the category of the turbulence synthesis method, the appropriate values of several parameters in the mathematical model were systematically studied. Detailed parameter sensitivity analyses were conducted to investigate several key parameters, including the sampling frequency intervals Δƒ, the introduced time scale factor τ0, the introduced spatial scale factor θ, the decay coefficient cj and the tuning factor γj, on the simulated turbulent fluctuating wind velocity spectra, the RMS values as well as the spatial correlations. Based on it, a serials of model parameters corresponding to four typical standard wind terrains defined in Chinese building code were then proposed in order to build a ‘standard numerical wind terrain model’. Numerical simulations and equilibrium state verifications for those standard wind fields were subsequently performed. The results showed that key parameters had significant impacts on the numerical reconstructions of the turbulent wind fields by employing NSRFG method, and the proposed standard numerical wind terrain models would be referential for similar LES research of building structures.