下击暴流非平稳脉动风速数值模拟

摘要

Distinct from the atmospheric boundary layer wind,the average wind speed of downburst has observable time-varying characteristics,and the fluctuating part of the wind speed of downburst possesses strongly non-stationary characteristics.According to the evolutionary spectrum theory,for effectively simulating the non-stationary fluctuating wind,it is neccessary to establish a non-uniform modulation function of the power spectrum and to provide an efficient simulation method of non-stationary wind speed.To do this,the method to create Kaimal non-uniform modulation function was used to obtain other appropriate modulation functions of power spectra,such as Davenport,Simiu and Harris, providing the precondition for simulating non-stationary fluctuating wind.Then,founded on the autoregressive (AR) model to further consider the time variability,a time-varying autoregressive (TAR)model was established,providing an effectual method for non-stationary wind speed simulation.Based on the precondition and method mentioned above,the non-stationary fluctuating wind speed of downburst was simulated in consideration of the time-varying features of the average wind speed.The simulation results show:for the non-stationary fluctuating wind speed of downburst,the cross-correlation weakens along with the increase of distance between different positions,and the amplitude increases with the increase of time-dependent average wind speed,which coincides with the actual wind field characteristics and indicates the effectiveness of non-uniform modulation function;the power spectrum has obvious time-varying characteristics which matches well with the target time-varying spectrum,and the temporal average power spectrum and correlation function are also in agreement with the targets,which indicate the efficiency of the method generating non-stationary fluctuating wind of downburst.%针对大气边界层近地风不同、下击暴流平均风速具有明显时变性及脉动风速具有较强非平稳特征，通过Kaimal非均匀调制函数的建立方法，获得Davenport调制函数、Simiu调制函数、Harris调制函数，为有效实现非平稳脉动风速模拟提供首要条件；考虑自回归AR模型时变性，建立非平稳随机过程TAR时变模型，为实现非平稳脉动风速模拟提供有效方法；考虑下击暴流平均风速时变特征，对下击暴流非平稳脉动风速进行模拟。结果表明，模拟的下击暴流非平稳脉动风速相关性随不同位置间距增大而减弱，振幅随时变平均风速增大而增大，与实际风场特性吻合，表明非均匀调制函数有效；功率谱时变特征明显，与目标时变谱时变特征吻合，且样本统计平均功率谱、相关函数与目标均吻合，表明下击暴流非平稳脉动风速模拟方法有效。