关于风洞中用尖劈和粗糙元模拟大气边界层的讨论

尖劈和粗糙元广泛地应用于风洞试验中的大气边界层模拟,该技术成功模拟了不同地貌特征的平均风速和湍流度剖面。随着风工程研究的深入,了解尖劈和粗糙元模拟过程中的作用机理有助于准确地模拟各种大气边界层湍流功率谱和尺度特性。试验表明:尖劈利用其迎风平板的分离流产生湍流涡旋,迎风板的宽度决定了涡旋的大小和湍流脉动强度,同时迎风板阻塞比沿高度递减产生近似线性的风速剖面;粗糙元用于模拟实际地面的摩擦效应,调整平均风速和湍流度的剖面分布。遗憾的是,尖劈下宽上窄的结构特点决定了该技术模拟的湍流功率谱和积分尺度的高度变化律与实际大气边界层相反。基于对模拟机理的认识,异型尖劈上部形状有助于模拟大比例模型试验要求的湍流风场。

Discussion on the simulation of atmospheric boundary layer with spires and roughness elements in wind tunnels

The Spires and roughness elements are most widely used to simulate the atmospheric boundary layer in wind tunnel experiments and have successfully simulated the profiles of wind speed and turbulence intensity for various terrains. With the further development of wind engineering, it is helpful to understand the mechanism of this technique so as to accurately simulate the power spectral density and integral scale of turbulence. Some tests show that spires behave as vortex generators by flow separation on the edges of their windward plate, meanwhile, their linear decrease of blockage with height brings about a corresponding linear wind profile downstream. Roughness elements physically simulate the roughness on earth surface and adjust the profiles of wind speed and turbulence intensity in wind tunnel. However, it is obvious that the profiles of simulated power spectra and integral scales with height are contrary to those in natural atmospheric boundary layer. Based on the knowledge of the mechanism, an improved spire shape has been proposed to simulate the required turbulence profiles for rather large scaled model tests.