Large-eddy simulation of the upslope boundary layer

Large-eddy simulation of the upslope boundary layer
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上坡边界层大涡模拟

DOI：
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发表时间：
2006
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影响因子：
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通讯作者：
U. Schumann
U. Schumann
中科院分区：
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文献类型：
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作者：
U. Schumann;U. Schumann

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采用大涡模拟（LES）方法，确定了静止分层大气下均匀加热的倾斜或垂直平面上形成的稳态上坡边界层（UBL）的湍流结构。在适当的尺度下，问题仅取决于坡度角a和相对于长度尺度H的表面粗糙度高度zo，这是分层和表面加热的函数。我们通过一系列的LESS覆盖了2”s a s 90”和3 x s z o / c 3 x 10b。使用不同网格的仿真表明，结果对截断误差的敏感性较弱。UBL通过缓慢衰减振荡接近稳态平均剖面；它的频率等于Brunt-Vaisala频率乘以sin a。在LES中，通过根据积分稳态条件调整场来实现向稳态收敛。对于G lo”，形成一个混合良好的层，在UBL外缘形成强烈的逆温和强烈的下坡流动。大尺度相干性较弱，在小倾角时存在横辊，在陡坡时存在纵辊。以坡角和表面粗糙度的函数形式列出了几个平均量，并给出了近似的幂律。平均量对坡角的依赖很难用简单的模型来解释，但表面粗糙度的影响与先前的结果密切相关。
Large-eddy simulation (LES) is used to determine the turbulent structure of the steady-state up-slope boundary layer (UBL) which forms at a uniformly heated inclined or vertical plane surface below a stratified atmosphere at rest. At proper scales, the problem depends solely on the slope angle a and the surface roughness height zo relative to a length scale H which is a function of stratification and surface heating. We cover 2" s a s 90" and 3 x S z o / c s 3 x 10b y a series of LESS. Simulations using different grids show that the results are only weakly sensitive to truncation errors. The UBL approaches a steady-state mean-profile by slowly decaying oscillations; its frequency equals the Brunt-Vaisala frequency times sin a. In the LES, convergence towards steady state has been enforced by adjusting the fields according to integral steady-state conditions. For a G lo", a well-mixed layer is formed which causes a strong temperature inversion and strong down-slope flow at the outer edge of the UBL. Large-scale coherence is weak with some indications of crossslope rolls for small inclination angles and longitudinal rolls for steep slopes. Several mean quantities have been tabulated as a function of slope angle and surface roughness and approximating power laws are given. The dependence of mean quantities on the slope angle is difficult to explain with simple models, but the influence of surface roughness closely follows earlier results.